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Misha Brukmanc1449e62008-12-10 23:07:02 +0000[diff] [blame]6 <title>LLVM Coding Standards</title>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]7</head>
8<body>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]9
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]10<div class="doc_title">
Misha Brukmanc1449e62008-12-10 23:07:02 +0000[diff] [blame]11 LLVM Coding Standards
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]12</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]13
14<ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner7ae36bb2001-07-23 20:40:41 +0000[diff] [blame]16 <li><a href="#mechanicalissues">Mechanical Source Issues</a>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]17 <ol>
18 <li><a href="#sourceformating">Source Code Formatting</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]19 <ol>
20 <li><a href="#scf_commenting">Commenting</a></li>
21 <li><a href="#scf_commentformat">Comment Formatting</a></li>
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]22 <li><a href="#scf_includes"><tt>#include</tt> Style</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]23 <li><a href="#scf_codewidth">Source Code Width</a></li>
24 <li><a href="#scf_spacestabs">Use Spaces Instead of Tabs</a></li>
25 <li><a href="#scf_indentation">Indent Code Consistently</a></li>
26 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]27 <li><a href="#compilerissues">Compiler Issues</a>
28 <ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]29 <li><a href="#ci_warningerrors">Treat Compiler Warnings Like
30 Errors</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]31 <li><a href="#ci_portable_code">Write Portable Code</a></li>
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]32 <li><a href="#ci_class_struct">Use of class/struct Keywords</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]33 </ol></li>
34 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]35 <li><a href="#styleissues">Style Issues</a>
36 <ol>
37 <li><a href="#macro">The High Level Issues</a>
38 <ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]39 <li><a href="#hl_module">A Public Header File <b>is</b> a
40 Module</a></li>
41 <li><a href="#hl_dontinclude">#include as Little as Possible</a></li>
42 <li><a href="#hl_privateheaders">Keep "internal" Headers
43 Private</a></li>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]44 <li><a href="#hl_earlyexit">Use Early Exits and 'continue' to Simplify
45 Code</a></li>
46 <li><a href="#hl_predicateloops">Turn Predicate Loops into Predicate
47 Functions</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]48 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]49 <li><a href="#micro">The Low Level Issues</a>
50 <ol>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]51 <li><a href="#ll_assert">Assert Liberally</a></li>
52 <li><a href="#ll_ns_std">Do not use 'using namespace std'</a></li>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]53 <li><a href="#ll_virtual_anch">Provide a virtual method anchor for
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]54 classes in headers</a></li>
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]55 <li><a href="#ll_end">Don't evaluate end() every time through a
56 loop</a></li>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]57 <li><a href="#ll_iostream"><tt>#include &lt;iostream&gt;</tt> is
58 <em>forbidden</em></a></li>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]59 <li><a href="#ll_avoidendl">Avoid <tt>std::endl</tt></a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]60 </ol></li>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]61
62 <li><a href="#nano">Microscopic Details</a>
63 <ol>
64 <li><a href="#micro_spaceparen">Spaces Before Parentheses</a></li>
65 <li><a href="#micro_preincrement">Prefer Preincrement</a></li>
66 <li><a href="#micro_namespaceindent">Namespace Indentation</a></li>
67 <li><a href="#micro_anonns">Anonymous Namespaces</a></li>
68 </ol></li>
69
70
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]71 </ol></li>
72 <li><a href="#seealso">See Also</a></li>
73</ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]74
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]75<div class="doc_author">
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]76 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
77 <a href="mailto:void@nondot.org">Bill Wendling</a></p>
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]78</div>
79
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]80
81<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]82<div class="doc_section">
83 <a name="introduction">Introduction</a>
84</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]85<!-- *********************************************************************** -->
86
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]87<div class="doc_text">
88
89<p>This document attempts to describe a few coding standards that are being used
90in the LLVM source tree. Although no coding standards should be regarded as
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]91absolute requirements to be followed in all instances, coding standards can be
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]92useful.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]93
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]94<p>This document intentionally does not prescribe fixed standards for religious
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]95issues such as brace placement and space usage. For issues like this, follow
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]96the golden rule:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]97
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]98<blockquote>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]99
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]100<p><b><a name="goldenrule">If you are adding a significant body of source to a
101project, feel free to use whatever style you are most comfortable with. If you
102are extending, enhancing, or bug fixing already implemented code, use the style
103that is already being used so that the source is uniform and easy to
104follow.</a></b></p>
105
106</blockquote>
107
108<p>The ultimate goal of these guidelines is the increase readability and
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]109maintainability of our common source base. If you have suggestions for topics to
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]110be included, please mail them to <a
111href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]112
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]113</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]114
115<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]116<div class="doc_section">
117 <a name="mechanicalissues">Mechanical Source Issues</a>
118</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]119<!-- *********************************************************************** -->
120
121<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]122<div class="doc_subsection">
123 <a name="sourceformating">Source Code Formatting</a>
124</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]125
126<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]127<div class="doc_subsubsection">
128 <a name="scf_commenting">Commenting</a>
129</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]130
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]131<div class="doc_text">
132
133<p>Comments are one critical part of readability and maintainability. Everyone
Chris Lattnerb927ca82009-07-12 00:10:24 +0000[diff] [blame]134knows they should comment, so should you. When writing comments, write them as
135English prose, which means they should use proper capitalization, punctuation,
136etc. Although we all should probably
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]137comment our code more than we do, there are a few very critical places that
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]138documentation is very useful:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]139
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]140<b>File Headers</b>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]141
Reid Spencer669ed452007-07-09 08:04:31 +0000[diff] [blame]142<p>Every source file should have a header on it that describes the basic
143purpose of the file. If a file does not have a header, it should not be
144checked into Subversion. Most source trees will probably have a standard
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]145file header format. The standard format for the LLVM source tree looks like
146this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]147
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]148<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]149<pre>
Chris Lattnerc49fcd12003-10-13 14:58:11 +0000[diff] [blame]150//===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
Misha Brukman98117cd2009-01-02 16:58:42 +0000[diff] [blame]151//
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]152// The LLVM Compiler Infrastructure
153//
Chris Lattnerab2b10c2007-12-29 19:56:08 +0000[diff] [blame]154// This file is distributed under the University of Illinois Open Source
155// License. See LICENSE.TXT for details.
Misha Brukman98117cd2009-01-02 16:58:42 +0000[diff] [blame]156//
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]157//===----------------------------------------------------------------------===//
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]158//
159// This file contains the declaration of the Instruction class, which is the
160// base class for all of the VM instructions.
161//
162//===----------------------------------------------------------------------===//
163</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]164</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]165
Chris Lattnerab2b10c2007-12-29 19:56:08 +0000[diff] [blame]166<p>A few things to note about this particular format: The "<tt>-*- C++
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]167-*-</tt>" string on the first line is there to tell Emacs that the source file
Misha Brukman69c58892004-07-28 22:37:57 +0000[diff] [blame]168is a C++ file, not a C file (Emacs assumes .h files are C files by default).
169Note that this tag is not necessary in .cpp files. The name of the file is also
170on the first line, along with a very short description of the purpose of the
171file. This is important when printing out code and flipping though lots of
172pages.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]173
Chris Lattnerab2b10c2007-12-29 19:56:08 +0000[diff] [blame]174<p>The next section in the file is a concise note that defines the license
175that the file is released under. This makes it perfectly clear what terms the
176source code can be distributed under and should not be modified in any way.</p>
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]177
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]178<p>The main body of the description does not have to be very long in most cases.
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]179Here it's only two lines. If an algorithm is being implemented or something
180tricky is going on, a reference to the paper where it is published should be
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]181included, as well as any notes or "gotchas" in the code to watch out for.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]182
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]183<b>Class overviews</b>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]184
Jim Laskeyf55914a2006-07-31 20:18:49 +0000[diff] [blame]185<p>Classes are one fundamental part of a good object oriented design. As such,
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]186a class definition should have a comment block that explains what the class is
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]187used for... if it's not obvious. If it's so completely obvious your grandma
188could figure it out, it's probably safe to leave it out. Naming classes
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]189something sane goes a long ways towards avoiding writing documentation.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]190
191
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]192<b>Method information</b>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]193
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]194<p>Methods defined in a class (as well as any global functions) should also be
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]195documented properly. A quick note about what it does any a description of the
196borderline behaviour is all that is necessary here (unless something
197particularly tricky or insideous is going on). The hope is that people can
198figure out how to use your interfaces without reading the code itself... that is
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]199the goal metric.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]200
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]201<p>Good things to talk about here are what happens when something unexpected
202happens: does the method return null? Abort? Format your hard disk?</p>
203
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]204</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]205
206<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]207<div class="doc_subsubsection">
208 <a name="scf_commentformat">Comment Formatting</a>
209</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]210
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]211<div class="doc_text">
212
213<p>In general, prefer C++ style (<tt>//</tt>) comments. They take less space,
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]214require less typing, don't have nesting problems, etc. There are a few cases
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]215when it is useful to use C style (<tt>/* */</tt>) comments however:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]216
217<ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]218 <li>When writing a C code: Obviously if you are writing C code, use C style
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]219 comments.</li>
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]220 <li>When writing a header file that may be <tt>#include</tt>d by a C source
221 file.</li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]222 <li>When writing a source file that is used by a tool that only accepts C
223 style comments.</li>
224</ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]225
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]226<p>To comment out a large block of code, use <tt>#if 0</tt> and <tt>#endif</tt>.
227These nest properly and are better behaved in general than C style comments.</p>
228
229</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]230
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]231<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]232<div class="doc_subsubsection">
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]233 <a name="scf_includes"><tt>#include</tt> Style</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]234</div>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]235
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]236<div class="doc_text">
237
238<p>Immediately after the <a href="#scf_commenting">header file comment</a> (and
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]239include guards if working on a header file), the <a
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]240href="#hl_dontinclude">minimal</a> list of <tt>#include</tt>s required by the
241file should be listed. We prefer these <tt>#include</tt>s to be listed in this
242order:</p>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]243
244<ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]245 <li><a href="#mmheader">Main Module header</a></li>
246 <li><a href="#hl_privateheaders">Local/Private Headers</a></li>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]247 <li><tt>llvm/*</tt></li>
248 <li><tt>llvm/Analysis/*</tt></li>
249 <li><tt>llvm/Assembly/*</tt></li>
250 <li><tt>llvm/Bytecode/*</tt></li>
251 <li><tt>llvm/CodeGen/*</tt></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]252 <li>...</li>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]253 <li><tt>Support/*</tt></li>
254 <li><tt>Config/*</tt></li>
255 <li>System <tt>#includes</tt></li>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]256</ol>
257
Nick Lewycky822293a2008-11-29 20:13:25 +0000[diff] [blame]258<p>... and each category should be sorted by name.</p>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]259
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]260<p><a name="mmheader">The "Main Module Header"</a> file applies to .cpp file
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]261which implement an interface defined by a .h file. This <tt>#include</tt>
262should always be included <b>first</b> regardless of where it lives on the file
263system. By including a header file first in the .cpp files that implement the
264interfaces, we ensure that the header does not have any hidden dependencies
265which are not explicitly #included in the header, but should be. It is also a
266form of documentation in the .cpp file to indicate where the interfaces it
267implements are defined.</p>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]268
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]269</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]270
271<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]272<div class="doc_subsubsection">
273 <a name="scf_codewidth">Source Code Width</a>
274</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]275
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]276<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]277
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]278<p>Write your code to fit within 80 columns of text. This helps those of us who
279like to print out code and look at your code in an xterm without resizing
280it.</p>
281
Chris Lattner5822e9e2008-07-08 05:12:37 +0000[diff] [blame]282<p>The longer answer is that there must be some limit to the width of the code
283in order to reasonably allow developers to have multiple files side-by-side in
284windows on a modest display. If you are going to pick a width limit, it is
285somewhat arbitrary but you might as well pick something standard. Going with
28690 columns (for example) instead of 80 columns wouldn't add any significant
287value and would be detrimental to printing out code. Also many other projects
288have standardized on 80 columns, so some people have already configured their
289editors for it (vs something else, like 90 columns).</p>
290
291<p>This is one of many contentious issues in coding standards, but is not up
292for debate.</p>
293
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]294</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]295
296<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]297<div class="doc_subsubsection">
298 <a name="scf_spacestabs">Use Spaces Instead of Tabs</a>
299</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]300
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]301<div class="doc_text">
302
303<p>In all cases, prefer spaces to tabs in source files. People have different
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]304prefered indentation levels, and different styles of indentation that they
305like... this is fine. What isn't is that different editors/viewers expand tabs
306out to different tab stops. This can cause your code to look completely
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]307unreadable, and it is not worth dealing with.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]308
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]309<p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]310style of existing code if your are modifying and extending it. If you like four
311spaces of indentation, <b>DO NOT</b> do that in the middle of a chunk of code
312with two spaces of indentation. Also, do not reindent a whole source file: it
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]313makes for incredible diffs that are absolutely worthless.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]314
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]315</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]316
317<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]318<div class="doc_subsubsection">
319 <a name="scf_indentation">Indent Code Consistently</a>
320</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]321
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]322<div class="doc_text">
323
324<p>Okay, your first year of programming you were told that indentation is
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]325important. If you didn't believe and internalize this then, now is the time.
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]326Just do it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]327
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]328</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]329
330
331<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]332<div class="doc_subsection">
333 <a name="compilerissues">Compiler Issues</a>
334</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]335
336
337<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]338<div class="doc_subsubsection">
339 <a name="ci_warningerrors">Treat Compiler Warnings Like Errors</a>
340</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]341
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]342<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]343
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]344<p>If your code has compiler warnings in it, something is wrong: you aren't
345casting values correctly, your have "questionable" constructs in your code, or
346you are doing something legitimately wrong. Compiler warnings can cover up
347legitimate errors in output and make dealing with a translation unit
348difficult.</p>
349
350<p>It is not possible to prevent all warnings from all compilers, nor is it
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]351desirable. Instead, pick a standard compiler (like <tt>gcc</tt>) that provides
352a good thorough set of warnings, and stick to them. At least in the case of
353<tt>gcc</tt>, it is possible to work around any spurious errors by changing the
354syntax of the code slightly. For example, an warning that annoys me occurs when
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]355I write code like this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]356
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]357<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]358<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]359if (V = getValue()) {
360 ...
361}
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]362</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]363</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]364
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]365<p><tt>gcc</tt> will warn me that I probably want to use the <tt>==</tt>
366operator, and that I probably mistyped it. In most cases, I haven't, and I
367really don't want the spurious errors. To fix this particular problem, I
368rewrite the code like this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]369
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]370<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]371<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]372if ((V = getValue())) {
373 ...
374}
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]375</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]376</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]377
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]378<p>...which shuts <tt>gcc</tt> up. Any <tt>gcc</tt> warning that annoys you can
379be fixed by massaging the code appropriately.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]380
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]381<p>These are the <tt>gcc</tt> warnings that I prefer to enable: <tt>-Wall
382-Winline -W -Wwrite-strings -Wno-unused</tt></p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]383
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]384</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]385
386<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]387<div class="doc_subsubsection">
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]388 <a name="ci_portable_code">Write Portable Code</a>
389</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]390
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]391<div class="doc_text">
392
393<p>In almost all cases, it is possible and within reason to write completely
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]394portable code. If there are cases where it isn't possible to write portable
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]395code, isolate it behind a well defined (and well documented) interface.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]396
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]397<p>In practice, this means that you shouldn't assume much about the host
398compiler, including its support for "high tech" features like partial
Chris Lattner4bd3d7e2009-03-23 04:52:53 +0000[diff] [blame]399specialization of templates. If these features are used, they should only be
400an implementation detail of a library which has a simple exposed API.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]401
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]402</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]403
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]404<!-- _______________________________________________________________________ -->
405<div class="doc_subsubsection">
406<a name="ci_class_struct">Use of <tt>class</tt> and <tt>struct</tt> Keywords</a>
407</div>
408<div class="doc_text">
Misha Brukmanedcc78a2004-10-26 15:45:13 +0000[diff] [blame]409
410<p>In C++, the <tt>class</tt> and <tt>struct</tt> keywords can be used almost
411interchangeably. The only difference is when they are used to declare a class:
412<tt>class</tt> makes all members private by default while <tt>struct</tt> makes
413all members public by default.</p>
414
415<p>Unfortunately, not all compilers follow the rules and some will generate
416different symbols based on whether <tt>class</tt> or <tt>struct</tt> was used to
417declare the symbol. This can lead to problems at link time.</p>
418
419<p>So, the rule for LLVM is to always use the <tt>class</tt> keyword, unless
420<b>all</b> members are public, in which case <tt>struct</tt> is allowed.</p>
421
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]422</div>
423
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]424<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]425<div class="doc_section">
426 <a name="styleissues">Style Issues</a>
427</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]428<!-- *********************************************************************** -->
429
430
431<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]432<div class="doc_subsection">
433 <a name="macro">The High Level Issues</a>
434</div>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]435<!-- ======================================================================= -->
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]436
437
438<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]439<div class="doc_subsubsection">
440 <a name="hl_module">A Public Header File <b>is</b> a Module</a>
441</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]442
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]443<div class="doc_text">
444
445<p>C++ doesn't do too well in the modularity department. There is no real
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]446encapsulation or data hiding (unless you use expensive protocol classes), but it
447is what we have to work with. When you write a public header file (in the LLVM
448source tree, they live in the top level "include" directory), you are defining a
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]449module of functionality.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]450
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]451<p>Ideally, modules should be completely independent of each other, and their
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]452header files should only include the absolute minimum number of headers
453possible. A module is not just a class, a function, or a namespace: <a
454href="http://www.cuj.com/articles/2000/0002/0002c/0002c.htm">it's a collection
455of these</a> that defines an interface. This interface may be several
456functions, classes or data structures, but the important issue is how they work
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]457together.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]458
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]459<p>In general, a module should be implemented with one or more <tt>.cpp</tt>
460files. Each of these <tt>.cpp</tt> files should include the header that defines
461their interface first. This ensure that all of the dependences of the module
462header have been properly added to the module header itself, and are not
463implicit. System headers should be included after user headers for a
464translation unit.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]465
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]466</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]467
468<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]469<div class="doc_subsubsection">
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]470 <a name="hl_dontinclude"><tt>#include</tt> as Little as Possible</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]471</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]472
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]473<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]474
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]475<p><tt>#include</tt> hurts compile time performance. Don't do it unless you
476have to, especially in header files.</p>
477
478<p>But wait, sometimes you need to have the definition of a class to use it, or
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]479to inherit from it. In these cases go ahead and <tt>#include</tt> that header
480file. Be aware however that there are many cases where you don't need to have
481the full definition of a class. If you are using a pointer or reference to a
482class, you don't need the header file. If you are simply returning a class
483instance from a prototyped function or method, you don't need it. In fact, for
484most cases, you simply don't need the definition of a class... and not
485<tt>#include</tt>'ing speeds up compilation.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]486
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]487<p>It is easy to try to go too overboard on this recommendation, however. You
Chris Lattner5da59b12007-02-10 18:35:31 +0000[diff] [blame]488<b>must</b> include all of the header files that you are using -- you can
489include them either directly
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]490or indirectly (through another header file). To make sure that you don't
491accidently forget to include a header file in your module header, make sure to
492include your module header <b>first</b> in the implementation file (as mentioned
493above). This way there won't be any hidden dependencies that you'll find out
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]494about later...</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]495
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]496</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]497
498<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]499<div class="doc_subsubsection">
500 <a name="hl_privateheaders">Keep "internal" Headers Private</a>
501</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]502
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]503<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]504
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]505<p>Many modules have a complex implementation that causes them to use more than
506one implementation (<tt>.cpp</tt>) file. It is often tempting to put the
507internal communication interface (helper classes, extra functions, etc) in the
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]508public module header file. Don't do this.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]509
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]510<p>If you really need to do something like this, put a private header file in
511the same directory as the source files, and include it locally. This ensures
512that your private interface remains private and undisturbed by outsiders.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]513
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]514<p>Note however, that it's okay to put extra implementation methods a public
515class itself... just make them private (or protected), and all is well.</p>
516
517</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]518
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]519<!-- _______________________________________________________________________ -->
520<div class="doc_subsubsection">
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]521 <a name="hl_earlyexit">Use Early Exits and 'continue' to Simplify Code</a>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]522</div>
523
524<div class="doc_text">
525
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]526<p>When reading code, keep in mind how much state and how many previous
527decisions have to be remembered by the reader to understand a block of code.
528Aim to reduce indentation where possible when it doesn't make it more difficult
529to understand the code. One great way to do this is by making use of early
530exits and the 'continue' keyword in long loops. As an example of using an early
531exit from a function, consider this "bad" code:</p>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]532
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]533<div class="doc_code">
534<pre>
535Value *DoSomething(Instruction *I) {
536 if (!isa&lt;TerminatorInst&gt;(I) &amp;&amp;
537 I-&gt;hasOneUse() &amp;&amp; SomeOtherThing(I)) {
538 ... some long code ....
539 }
540
541 return 0;
542}
543</pre>
544</div>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]545
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]546<p>This code has several problems if the body of the 'if' is large. When you're
547looking at the top of the function, it isn't immediately clear that this
548<em>only</em> does interesting things with non-terminator instructions, and only
549applies to things with the other predicates. Second, it is relatively difficult
550to describe (in comments) why these predicates are important because the if
551statement makes it difficult to lay out the comments. Third, when you're deep
552within the body of the code, it is indented an extra level. Finally, when
553reading the top of the function, it isn't clear what the result is if the
554predicate isn't true, you have to read to the end of the function to know that
555it returns null.</p>
Matthijs Kooijmaned58a972008-07-30 12:14:10 +0000[diff] [blame]556
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]557<p>It is much preferred to format the code like this:</p>
558
559<div class="doc_code">
560<pre>
561Value *DoSomething(Instruction *I) {
562 // Terminators never need 'something' done to them because, ...
563 if (isa&lt;TerminatorInst&gt;(I))
564 return 0;
565
566 // We conservatively avoid transforming instructions with multiple uses
567 // because goats like cheese.
568 if (!I-&gt;hasOneUse())
569 return 0;
570
571 // This is really just here for example.
572 if (!SomeOtherThing(I))
573 return 0;
574
575 ... some long code ....
576}
577</pre>
578</div>
579
580<p>This fixes these problems. A similar problem frequently happens in for
581loops. A silly example is something like this:</p>
582
583<div class="doc_code">
584<pre>
585 for (BasicBlock::iterator II = BB-&gt;begin(), E = BB-&gt;end(); II != E; ++II) {
586 if (BinaryOperator *BO = dyn_cast&lt;BinaryOperator&gt;(II)) {
587 Value *LHS = BO-&gt;getOperand(0);
588 Value *RHS = BO-&gt;getOperand(1);
589 if (LHS != RHS) {
590 ...
591 }
592 }
593 }
594</pre>
595</div>
596
597<p>When you have very very small loops, this sort of structure is fine, but if
598it exceeds more than 10-15 lines, it becomes difficult for people to read and
599understand at a glance.
600The problem with this sort of code is that it gets very nested very quickly,
601meaning that the reader of the code has to keep a lot of context in their brain
602to remember what is going immediately on in the loop, because they don't know
603if/when the if conditions will have elses etc. It is strongly preferred to
604structure the loop like this:</p>
605
606<div class="doc_code">
607<pre>
608 for (BasicBlock::iterator II = BB-&gt;begin(), E = BB-&gt;end(); II != E; ++II) {
609 BinaryOperator *BO = dyn_cast&lt;BinaryOperator&gt;(II);
610 if (!BO) continue;
611
612 Value *LHS = BO-&gt;getOperand(0);
613 Value *RHS = BO-&gt;getOperand(1);
614 if (LHS == RHS) continue;
615 }
616</pre>
617</div>
618
619<p>This has all the benefits of using early exits from functions: it reduces
620nesting of the loop, it makes it easier to describe why the conditions are true,
621and it makes it obvious to the reader that there is no "else" coming up that
622they have to push context into their brain for. If a loop is large, this can
623be a big understandability win.</p>
624
625</div>
626
627
628<!-- _______________________________________________________________________ -->
629<div class="doc_subsubsection">
630 <a name="hl_predicateloops">Turn Predicate Loops into Predicate Functions</a>
631</div>
632
633<div class="doc_text">
634
635<p>It is very common to write inline functions that just compute a boolean
636 value. There are a number of ways that people commonly write these, but an
637 example of this sort of thing is:</p>
638
639<div class="doc_code">
640<pre>
641 <b>bool FoundFoo = false;</b>
642 for (unsigned i = 0, e = BarList.size(); i != e; ++i)
643 if (BarList[i]-&gt;isFoo()) {
644 <b>FoundFoo = true;</b>
645 break;
646 }
647
648 <b>if (FoundFoo) {</b>
649 ...
650 }
651</pre>
652</div>
653
654<p>This sort of code is awkward to write, and is almost always a bad sign.
655Instead of this sort of loop, we strongly prefer to use a predicate function
656(which may be <a href="#micro_anonns">static</a>) that uses
657<a href="#hl_earlyexit">early exits</a> to compute the predicate. Code like
658this would be preferred:
659</p>
660
661
662<div class="doc_code">
663<pre>
664/// ListContainsFoo - Return true if the specified list has an element that is
665/// a foo.
666static bool ListContainsFoo(const std::vector&lt;Bar*&gt; &amp;List) {
667 for (unsigned i = 0, e = List.size(); i != e; ++i)
668 if (List[i]-&gt;isFoo())
669 return true;
670 return false;
671}
672...
673
674 <b>if (ListContainsFoo(BarList)) {</b>
675 ...
676 }
677</pre>
678</div>
679
680<p>There are many reasons for doing this: it reduces indentation and factors out
681code which can often be shared by other code that checks for the same predicate.
682More importantly, it <em>forces you to pick a name</em> for the function, and
683forces you to write a comment for it. In this silly example, this doesn't add
684much value. However, if the condition is complex, this can make it a lot easier
685for the reader to understand the code that queries for this predicate. Instead
686of being faced with the in-line details of we check to see if the BarList
687contains a foo, we can trust the function name and continue reading with better
688locality.</p>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]689
690</div>
691
692
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]693<!-- ======================================================================= -->
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]694<div class="doc_subsection">
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]695 <a name="micro">The Low Level Issues</a>
696</div>
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]697<!-- ======================================================================= -->
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]698
699
700<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]701<div class="doc_subsubsection">
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]702 <a name="ll_assert">Assert Liberally</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]703</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]704
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]705<div class="doc_text">
706
707<p>Use the "<tt>assert</tt>" function to its fullest. Check all of your
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]708preconditions and assumptions, you never know when a bug (not neccesarily even
709yours) might be caught early by an assertion, which reduces debugging time
710dramatically. The "<tt>&lt;cassert&gt;</tt>" header file is probably already
711included by the header files you are using, so it doesn't cost anything to use
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]712it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]713
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]714<p>To further assist with debugging, make sure to put some kind of error message
715in the assertion statement (which is printed if the assertion is tripped). This
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]716helps the poor debugging make sense of why an assertion is being made and
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]717enforced, and hopefully what to do about it. Here is one complete example:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]718
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]719<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]720<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]721inline Value *getOperand(unsigned i) {
722 assert(i &lt; Operands.size() &amp;&amp; "getOperand() out of range!");
723 return Operands[i];
724}
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]725</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]726</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]727
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]728<p>Here are some examples:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]729
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]730<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]731<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]732assert(Ty-&gt;isPointerType() &amp;&amp; "Can't allocate a non pointer type!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]733
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]734assert((Opcode == Shl || Opcode == Shr) &amp;&amp; "ShiftInst Opcode invalid!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]735
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]736assert(idx &lt; getNumSuccessors() &amp;&amp; "Successor # out of range!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]737
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]738assert(V1.getType() == V2.getType() &amp;&amp; "Constant types must be identical!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]739
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]740assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!");
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]741</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]742</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]743
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]744<p>You get the idea...</p>
745
Nick Lewyckyf4408e82008-05-31 23:54:55 +0000[diff] [blame]746<p>Please be aware when adding assert statements that not all compilers are aware of
747the semantics of the assert. In some places, asserts are used to indicate a piece of
748code that should not be reached. These are typically of the form:</p>
749
750<div class="doc_code">
751<pre>
Dan Gohmanf0032762008-11-24 17:18:39 +0000[diff] [blame]752assert(0 &amp;&amp; "Some helpful error message");
Nick Lewyckyf4408e82008-05-31 23:54:55 +0000[diff] [blame]753</pre>
754</div>
755
756<p>When used in a function that returns a value, they should be followed with a return
757statement and a comment indicating that this line is never reached. This will prevent
758a compiler which is unable to deduce that the assert statement never returns from
759generating a warning.</p>
760
761<div class="doc_code">
762<pre>
Dan Gohmanf0032762008-11-24 17:18:39 +0000[diff] [blame]763assert(0 &amp;&amp; "Some helpful error message");
Nick Lewyckyf4408e82008-05-31 23:54:55 +0000[diff] [blame]764// Not reached
765return 0;
766</pre>
767</div>
768
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]769</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]770
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]771<!-- _______________________________________________________________________ -->
772<div class="doc_subsubsection">
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]773 <a name="ll_ns_std">Do not use '<tt>using namespace std</tt>'</a>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]774</div>
775
776<div class="doc_text">
777<p>In LLVM, we prefer to explicitly prefix all identifiers from the standard
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]778namespace with an "<tt>std::</tt>" prefix, rather than rely on
779"<tt>using namespace std;</tt>".</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]780
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]781<p> In header files, adding a '<tt>using namespace XXX</tt>' directive pollutes
Misha Brukman2d33c542008-12-11 19:37:04 +0000[diff] [blame]782the namespace of any source file that <tt>#include</tt>s the header. This is
783clearly a bad thing.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]784
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]785<p>In implementation files (e.g. .cpp files), the rule is more of a stylistic
786rule, but is still important. Basically, using explicit namespace prefixes
787makes the code <b>clearer</b>, because it is immediately obvious what facilities
788are being used and where they are coming from, and <b>more portable</b>, because
789namespace clashes cannot occur between LLVM code and other namespaces. The
790portability rule is important because different standard library implementations
791expose different symbols (potentially ones they shouldn't), and future revisions
792to the C++ standard will add more symbols to the <tt>std</tt> namespace. As
793such, we never use '<tt>using namespace std;</tt>' in LLVM.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]794
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]795<p>The exception to the general rule (i.e. it's not an exception for
796the <tt>std</tt> namespace) is for implementation files. For example, all of
797the code in the LLVM project implements code that lives in the 'llvm' namespace.
798As such, it is ok, and actually clearer, for the .cpp files to have a '<tt>using
799namespace llvm</tt>' directive at their top, after the <tt>#include</tt>s. The
800general form of this rule is that any .cpp file that implements code in any
801namespace may use that namespace (and its parents'), but should not use any
802others.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]803
804</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]805
806<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]807<div class="doc_subsubsection">
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]808 <a name="ll_virtual_anch">Provide a virtual method anchor for classes
809 in headers</a>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]810</div>
811
812<div class="doc_text">
813
814<p>If a class is defined in a header file and has a v-table (either it has
815virtual methods or it derives from classes with virtual methods), it must
816always have at least one out-of-line virtual method in the class. Without
Misha Brukman2d33c542008-12-11 19:37:04 +0000[diff] [blame]817this, the compiler will copy the vtable and RTTI into every <tt>.o</tt> file
818that <tt>#include</tt>s the header, bloating <tt>.o</tt> file sizes and
819increasing link times.</p>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]820
821</div>
822
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]823<!-- _______________________________________________________________________ -->
824<div class="doc_subsubsection">
825 <a name="ll_end">Don't evaluate end() every time through a loop</a>
826</div>
827
828<div class="doc_text">
829
830<p>Because C++ doesn't have a standard "foreach" loop (though it can be emulated
831with macros and may be coming in C++'0x) we end up writing a lot of loops that
832manually iterate from begin to end on a variety of containers or through other
833data structures. One common mistake is to write a loop in this style:</p>
834
835<div class="doc_code">
836<pre>
837 BasicBlock *BB = ...
838 for (BasicBlock::iterator I = BB->begin(); I != <b>BB->end()</b>; ++I)
839 ... use I ...
840</pre>
841</div>
842
843<p>The problem with this construct is that it evaluates "<tt>BB->end()</tt>"
844every time through the loop. Instead of writing the loop like this, we strongly
845prefer loops to be written so that they evaluate it once before the loop starts.
846A convenient way to do this is like so:</p>
847
848<div class="doc_code">
849<pre>
850 BasicBlock *BB = ...
851 for (BasicBlock::iterator I = BB->begin(), E = <b>BB->end()</b>; I != E; ++I)
852 ... use I ...
853</pre>
854</div>
855
856<p>The observant may quickly point out that these two loops may have different
857semantics: if the container (a basic block in this case) is being mutated, then
858"<tt>BB->end()</tt>" may change its value every time through the loop and the
859second loop may not in fact be correct. If you actually do depend on this
Chris Lattner09bc65e2009-06-30 06:20:03 +0000[diff] [blame]860behavior, please write the loop in the first form and add a comment indicating
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]861that you did it intentionally.</p>
862
863<p>Why do we prefer the second form (when correct)? Writing the loop in the
864first form has two problems: First it may be less efficient than evaluating it
865at the start of the loop. In this case, the cost is probably minor: a few extra
866loads every time through the loop. However, if the base expression is more
867complex, then the cost can rise quickly. I've seen loops where the end
868expression was actually something like: "<tt>SomeMap[x]->end()</tt>" and map
Chris Lattnera44f87f2009-06-30 06:27:54 +0000[diff] [blame]869lookups really aren't cheap. By writing it in the second form consistently, you
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]870eliminate the issue entirely and don't even have to think about it.</p>
871
Chris Lattner09bc65e2009-06-30 06:20:03 +0000[diff] [blame]872<p>The second (even bigger) issue is that writing the loop in the first form
Chris Lattner0af39ea2009-06-30 06:13:23 +0000[diff] [blame]873hints to the reader that the loop is mutating the container (a fact that a
874comment would handily confirm!). If you write the loop in the second form, it
875is immediately obvious without even looking at the body of the loop that the
876container isn't being modified, which makes it easier to read the code and
877understand what it does.</p>
878
879<p>While the second form of the loop is a few extra keystrokes, we do strongly
880prefer it.</p>
881
882</div>
883
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]884<!-- _______________________________________________________________________ -->
885<div class="doc_subsubsection">
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]886 <a name="ll_iostream"><tt>#include &lt;iostream&gt;</tt> is forbidden</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]887</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]888
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]889<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]890
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]891<p>The use of <tt>#include &lt;iostream&gt;</tt> in library files is
892hereby <b><em>forbidden</em></b>. The primary reason for doing this is to
893support clients using LLVM libraries as part of larger systems. In particular,
894we statically link LLVM into some dynamic libraries. Even if LLVM isn't used,
895the static c'tors are run whenever an application start up that uses the dynamic
896library. There are two problems with this:</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]897
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]898<ol>
899 <li>The time to run the static c'tors impacts startup time of
900 applications&mdash;a critical time for GUI apps.</li>
901 <li>The static c'tors cause the app to pull many extra pages of memory off the
902 disk: both the code for the static c'tors in each <tt>.o</tt> file and the
903 small amount of data that gets touched. In addition, touched/dirty pages
904 put more pressure on the VM system on low-memory machines.</li>
905</ol>
906
907<p>Note that using the other stream headers (<tt>&lt;sstream&gt;</tt> for
908example) is allowed normally, it is just <tt>&lt;iostream&gt;</tt> that is
909causing problems.</p>
910
911<p>The preferred replacement for stream functionality is the
912<tt>llvm::raw_ostream</tt> class (for writing to output streams of various
913sorts) and the <tt>llvm::MemoryBuffer</tt> API (for reading in files).</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]914
915</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]916
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]917
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]918<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]919<div class="doc_subsubsection">
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]920 <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]921</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]922
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]923<div class="doc_text">
924
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]925<p>The <tt>std::endl</tt> modifier, when used with iostreams outputs a newline
926to the output stream specified. In addition to doing this, however, it also
927flushes the output stream. In other words, these are equivalent:</p>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]928
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]929<div class="doc_code">
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]930<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]931std::cout &lt;&lt; std::endl;
932std::cout &lt;&lt; '\n' &lt;&lt; std::flush;
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]933</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]934</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]935
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]936<p>Most of the time, you probably have no reason to flush the output stream, so
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]937it's better to use a literal <tt>'\n'</tt>.</p>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]938
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]939</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]940
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]941
Chris Lattnerd283cb12009-07-22 05:40:54 +0000[diff] [blame^]942<!-- ======================================================================= -->
943<div class="doc_subsection">
944 <a name="nano">Microscopic Details</a>
945</div>
946<!-- ======================================================================= -->
947
948<p>This section describes preferred low-level formatting guidelines along with
949reasoning on why we prefer them.</p>
950
951<!-- _______________________________________________________________________ -->
952<div class="doc_subsubsection">
953 <a name="micro_spaceparen">Spaces Before Parentheses</a>
954</div>
955
956<div class="doc_text">
957
958<p>We prefer to put a space before a parentheses only in control flow
959statements, but not in normal function call expressions and function-like
960macros. For example, this is good:</p>
961
962<div class="doc_code">
963<pre>
964 <b>if (</b>x) ...
965 <b>for (</b>i = 0; i != 100; ++i) ...
966 <b>while (</b>llvm_rocks) ...
967
968 <b>somefunc(</b>42);
969 <b><a href="#ll_assert">assert</a>(</b>3 != 4 &amp;&amp; "laws of math are failing me");
970
971 a = <b>foo(</b>42, 92) + <b>bar(</b>x);
972 </pre>
973</div>
974
975<p>... and this is bad:</p>
976
977<div class="doc_code">
978<pre>
979 <b>if(</b>x) ...
980 <b>for(</b>i = 0; i != 100; ++i) ...
981 <b>while(</b>llvm_rocks) ...
982
983 <b>somefunc (</b>42);
984 <b><a href="#ll_assert">assert</a> (</b>3 != 4 &amp;&amp; "laws of math are failing me");
985
986 a = <b>foo (</b>42, 92) + <b>bar (</b>x);
987</pre>
988</div>
989
990<p>The reason for doing this is not completely arbitrary. This style makes
991 control flow operators stand out more, and makes expressions flow better. The
992 function call operator binds very tightly as a postfix operator. Putting
993 a space after a function name (as in the last example) makes it appear that
994 the code might bind the arguments of the left-hand-side of a binary operator
995 with the argument list of a function and the name of the right side. More
996 specifically, it is easy to misread the "a" example as:</p>
997
998<div class="doc_code">
999<pre>
1000 a = foo <b>(</b>(42, 92) + bar<b>)</b> (x);
1001</pre>
1002</div>
1003
1004<p>... when skimming through the code. By avoiding a space in a function, we
1005avoid this misinterpretation.</p>
1006
1007</div>
1008
1009<!-- _______________________________________________________________________ -->
1010<div class="doc_subsubsection">
1011 <a name="micro_preincrement">Prefer Preincrement</a>
1012</div>
1013
1014<div class="doc_text">
1015
1016<p>Hard fast rule: Preincrement (<tt>++X</tt>) may be no slower than
1017postincrement (<tt>X++</tt>) and could very well be a lot faster than it. Use
1018preincrementation whenever possible.</p>
1019
1020<p>The semantics of postincrement include making a copy of the value being
1021incremented, returning it, and then preincrementing the "work value". For
1022primitive types, this isn't a big deal... but for iterators, it can be a huge
1023issue (for example, some iterators contains stack and set objects in them...
1024copying an iterator could invoke the copy ctor's of these as well). In general,
1025get in the habit of always using preincrement, and you won't have a problem.</p>
1026
1027</div>
1028
1029<!-- _______________________________________________________________________ -->
1030<div class="doc_subsubsection">
1031 <a name="micro_namespaceindent">Namespace Indentation</a>
1032</div>
1033
1034<div class="doc_text">
1035
1036<p>
1037In general, we strive to reduce indentation where ever possible. This is useful
1038because we want code to <a href="#scf_codewidth">fit into 80 columns</a> without
1039wrapping horribly, but also because it makes it easier to understand the code.
1040Namespaces are a funny thing: they are often large, and we often desire to put
1041lots of stuff into them (so they can be large). Other times they are tiny,
1042because they just hold an enum or something similar. In order to balance this,
1043we use different approaches for small versus large namespaces.
1044</p>
1045
1046<p>
1047If a namespace definition is small and <em>easily</em> fits on a screen (say,
1048less than 35 lines of code), then you should indent its body. Here's an
1049example:
1050</p>
1051
1052<div class="doc_code">
1053<pre>
1054/// SomeCrazyThing - This namespace contains flags for ...
1055namespace SomeCrazyThing {
1056 enum foo {
1057 /// X - This is the X flag, which is ...
1058 X = 1,
1059
1060 /// Y - This is the Y flag, which is ...
1061 Y = 2,
1062
1063 /// Z - This is the Z flag, which is ...
1064 Z = 4,
1065
1066 /// ALL_FLAGS - This is the union of all flags.
1067 ALL_FLAGS = 7
1068 };
1069}
1070</pre>
1071</div>
1072
1073<p>Since the body is small, indenting adds value because it makes it very clear
1074where the namespace starts and ends, and it is easy to take the whole thing in
1075in one "gulp" when reading the code. If the blob of code in the namespace is
1076larger (as it typically is in a header in the llvm or clang namespaces), do not
1077indent the code, and add a comment indicating what namespace is being closed.
1078For example:</p>
1079
1080<div class="doc_code">
1081<pre>
1082namespace llvm {
1083namespace knowledge {
1084
1085/// Grokable - This class represents things that Smith can have an intimate
1086/// understanding of and contains the data associated with it.
1087class Grokable {
1088...
1089public:
1090 explicit Grokable() { ... }
1091 virtual ~Grokable() = 0;
1092
1093 ...
1094
1095};
1096
1097} // end namespace knowledge
1098} // end namespace llvm
1099</pre>
1100</div>
1101
1102<p>Because the class is large, we don't expect that the reader can easily
1103understand the entire concept in a glance, and the end of the file (where the
1104namespaces end) may be a long ways away from the place they open. As such,
1105indenting the contents of the namespace doesn't add any value, and detracts from
1106the readability of the class. In these cases it is best to <em>not</em> indent
1107the contents of the namespace.</p>
1108
1109</div>
1110
1111<!-- _______________________________________________________________________ -->
1112<div class="doc_subsubsection">
1113 <a name="micro_anonns">Anonymous Namespaces</a>
1114</div>
1115
1116<div class="doc_text">
1117
1118<p>A common topic after talking about namespaces is anonymous namespaces.
1119Anonymous namespaces are a great language feature that tells the C++ compiler
1120that the contents of the namespace are only visible within the current
1121translation unit, allowing more aggressive optimization and eliminating the
1122possibility of symbol name collisions. Anonymous namespaces are to C++ as
1123"static" is to C functions and global variables. While "static" is available
1124in C++, anonymous namespaces are more general: they can make entire classes
1125private to a file.</p>
1126
1127<p>The problem with anonymous namespaces is that they naturally want to
1128encourage indentation of their body, and they reduce locality of reference: if
1129you see a random function definition in a C++ file, it is easy to see if it is
1130marked static, but seeing if it is in an anonymous namespace requires scanning
1131a big chunk of the file.</p>
1132
1133<p>Because of this, we have a simple guideline: make anonymous namespaces as
1134small as possible, and only use them for class declarations. For example, this
1135is good:</p>
1136
1137<div class="doc_code">
1138<pre>
1139<b>namespace {</b>
1140 class StringSort {
1141 ...
1142 public:
1143 StringSort(...)
1144 bool operator&lt;(const char *RHS) const;
1145 };
1146<b>} // end anonymous namespace</b>
1147
1148static void Helper() {
1149 ...
1150}
1151
1152bool StringSort::operator&lt;(const char *RHS) const {
1153 ...
1154}
1155
1156</pre>
1157</div>
1158
1159<p>This is bad:</p>
1160
1161
1162<div class="doc_code">
1163<pre>
1164<b>namespace {</b>
1165class StringSort {
1166...
1167public:
1168 StringSort(...)
1169 bool operator&lt;(const char *RHS) const;
1170};
1171
1172void Helper() {
1173 ...
1174}
1175
1176bool StringSort::operator&lt;(const char *RHS) const {
1177 ...
1178}
1179
1180<b>} // end anonymous namespace</b>
1181
1182</pre>
1183</div>
1184
1185
1186<p>This is bad specifically because if you're looking at "Helper" in the middle
1187of a large C++ file, that you have no immediate way to tell if it is local to
1188the file. When it is marked static explicitly, this is immediately obvious.
1189Also, there is no reason to enclose the definition of "operator&lt;" in the
1190namespace since it was declared there.
1191</p>
1192
1193</div>
1194
1195
1196
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1197<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1198<div class="doc_section">
1199 <a name="seealso">See Also</a>
1200</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1201<!-- *********************************************************************** -->
1202
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1203<div class="doc_text">
1204
1205<p>A lot of these comments and recommendations have been culled for other
1206sources. Two particularly important books for our work are:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1207
1208<ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1209
Chris Lattner788ee282007-11-09 21:49:08 +0000[diff] [blame]1210<li><a href="http://www.amazon.com/Effective-Specific-Addison-Wesley-Professional-Computing/dp/0321334876">Effective
1211C++</a> by Scott Meyers. Also
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]1212interesting and useful are "More Effective C++" and "Effective STL" by the same
1213author.</li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1214
Chris Lattner788ee282007-11-09 21:49:08 +0000[diff] [blame]1215<li>Large-Scale C++ Software Design by John Lakos</li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1216
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1217</ol>
1218
1219<p>If you get some free time, and you haven't read them: do so, you might learn
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]1220something.</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1221
1222</div>
1223
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]1224<!-- *********************************************************************** -->
1225
1226<hr>
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]1227<address>
1228 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1232
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]1233 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]1234 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]1235 Last modified: $Date$
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]1236</address>
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