base/bind.h.pump

$$ This is a pump file for generating file templates.  Pump is a python
$$ script that is part of the Google Test suite of utilities.  Description
$$ can be found here:
$$
$$ http://code.google.com/p/googletest/wiki/PumpManual
$$

$$
$$ MAX_ARITY controls the number of arguments that Bind() supports.
$$ The amount of code, and more importantly, the number of template types
$$ generated by pump grows at O(MAX_ARITY^2).
$$
$$ We tried going to 11 and found it imposed an extra 10 penalty on windows
$$ cycle times compared to our original baseline of 6.
$$
$$ Currently 7 is chosen as a compromise between supporting a convenient
$$ number of arguments and keeping compile times low.  At 7, we have 115
$$ templates being generated by pump.
$$
$$ Be careful when adjusting this number.  If people find a need to bind
$$ a larger number of arguments, consider refactoring the function to use
$$ a param struct instead of raising the MAX_ARITY.
$$
$$ See http://crbug.com/98542 for more context.
$$
$var MAX_ARITY = 7

// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_BIND_H_
#define BASE_BIND_H_

#include "base/bind_internal.h"
#include "base/callback_internal.h"

// -----------------------------------------------------------------------------
// Usage documentation
// -----------------------------------------------------------------------------
//
// See base/callback.h for documentation.
//
//
// -----------------------------------------------------------------------------
// Implementation notes
// -----------------------------------------------------------------------------
//
// If you're reading the implementation, before proceeding further, you should
// read the top comment of base/bind_internal.h for a definition of common
// terms and concepts.
//
// RETURN TYPES
//
// Though Bind()'s result is meant to be stored in a Callback<> type, it
// cannot actually return the exact type without requiring a large amount
// of extra template specializations. The problem is that in order to
// discern the correct specialization of Callback<>, Bind would need to
// unwrap the function signature to determine the signature's arity, and
// whether or not it is a method.
//
// Each unique combination of (arity, function_type, num_prebound) where
// function_type is one of {function, method, const_method} would require
// one specialization.  We eventually have to do a similar number of
// specializations anyways in the implementation (see the Invoker<>,
// classes).  However, it is avoidable in Bind if we return the result
// via an indirection like we do below.
//
// TODO(ajwong): We might be able to avoid this now, but need to test.
//
// It is possible to move most of the COMPILE_ASSERT asserts into BindState<>,
// but it feels a little nicer to have the asserts here so people do not
// need to crack open bind_internal.h.  On the other hand, it makes Bind()
// harder to read.

namespace base {

$range ARITY 0..MAX_ARITY
$for ARITY [[
$range ARG 1..ARITY

template <typename Functor[[]]
$if ARITY > 0 [[, ]] $for ARG , [[typename P$(ARG)]]>
base::Callback<
    typename internal::BindState<
        typename internal::FunctorTraits<Functor>::RunnableType,
        typename internal::FunctorTraits<Functor>::RunType,
        void($for ARG , [[typename internal::CallbackParamTraits<P$(ARG)>::StorageType]])>
            ::UnboundRunType>
Bind(Functor functor
$if ARITY > 0 [[, ]] $for ARG , [[const P$(ARG)& p$(ARG)]]) {
  // Typedefs for how to store and run the functor.
  typedef typename internal::FunctorTraits<Functor>::RunnableType RunnableType;
  typedef typename internal::FunctorTraits<Functor>::RunType RunType;

  // Use RunnableType::RunType instead of RunType above because our
  // checks should below for bound references need to know what the actual
  // functor is going to interpret the argument as.
  typedef internal::FunctionTraits<typename RunnableType::RunType>
      BoundFunctorTraits;

$if ARITY > 0 [[

  // Do not allow binding a non-const reference parameter. Non-const reference
  // parameters are disallowed by the Google style guide.  Also, binding a
  // non-const reference parameter can make for subtle bugs because the
  // invoked function will receive a reference to the stored copy of the
  // argument and not the original.
  COMPILE_ASSERT(
      !($for ARG || [[
is_non_const_reference<typename BoundFunctorTraits::A$(ARG)Type>::value ]]),
      do_not_bind_functions_with_nonconst_ref);

]]


$for ARG [[


$if ARG == 1 [[
  // For methods, we need to be careful for parameter 1.  We do not require
  // a scoped_refptr because BindState<> itself takes care of AddRef() for
  // methods. We also disallow binding of an array as the method's target
  // object.
  COMPILE_ASSERT(
      internal::HasIsMethodTag<RunnableType>::value ||
          !internal::NeedsScopedRefptrButGetsRawPtr<P$(ARG)>::value,
      p$(ARG)_is_refcounted_type_and_needs_scoped_refptr);
  COMPILE_ASSERT(!internal::HasIsMethodTag<RunnableType>::value ||
                     !is_array<P$(ARG)>::value,
                 first_bound_argument_to_method_cannot_be_array);
]] $else [[
  COMPILE_ASSERT(!internal::NeedsScopedRefptrButGetsRawPtr<P$(ARG)>::value,
                 p$(ARG)_is_refcounted_type_and_needs_scoped_refptr);
]]  $$ $if ARG

]]  $$ $for ARG

  typedef internal::BindState<RunnableType, RunType, [[]]
void($for ARG , [[typename internal::CallbackParamTraits<P$(ARG)>::StorageType]])> [[]]
BindState;


  return Callback<typename BindState::UnboundRunType>(
      new BindState(internal::MakeRunnable(functor)[[]]
$if ARITY > 0 [[, ]] $for ARG , [[p$(ARG)]]));
}

]]  $$ for ARITY

}  // namespace base

#endif  // BASE_BIND_H_