Add the down_cast template.
Change-Id: Ib60c3fd1dfca3ba3fd0296633f3d96c992f790c8
diff --git a/src/casts.h b/src/casts.h
index 15852cf..cdb57ee 100644
--- a/src/casts.h
+++ b/src/casts.h
@@ -3,11 +3,66 @@
#ifndef ART_SRC_CASTS_H_
#define ART_SRC_CASTS_H_
+#include <assert.h>
#include <string.h>
#include "src/macros.h"
namespace art {
+// Use implicit_cast as a safe version of static_cast or const_cast
+// for upcasting in the type hierarchy (i.e. casting a pointer to Foo
+// to a pointer to SuperclassOfFoo or casting a pointer to Foo to
+// a const pointer to Foo).
+// When you use implicit_cast, the compiler checks that the cast is safe.
+// Such explicit implicit_casts are necessary in surprisingly many
+// situations where C++ demands an exact type match instead of an
+// argument type convertable to a target type.
+//
+// The From type can be inferred, so the preferred syntax for using
+// implicit_cast is the same as for static_cast etc.:
+//
+// implicit_cast<ToType>(expr)
+//
+// implicit_cast would have been part of the C++ standard library,
+// but the proposal was submitted too late. It will probably make
+// its way into the language in the future.
+template<typename To, typename From>
+inline To implicit_cast(From const &f) {
+ return f;
+}
+
+// When you upcast (that is, cast a pointer from type Foo to type
+// SuperclassOfFoo), it's fine to use implicit_cast<>, since upcasts
+// always succeed. When you downcast (that is, cast a pointer from
+// type Foo to type SubclassOfFoo), static_cast<> isn't safe, because
+// how do you know the pointer is really of type SubclassOfFoo? It
+// could be a bare Foo, or of type DifferentSubclassOfFoo. Thus,
+// when you downcast, you should use this macro. In debug mode, we
+// use dynamic_cast<> to double-check the downcast is legal (we die
+// if it's not). In normal mode, we do the efficient static_cast<>
+// instead. Thus, it's important to test in debug mode to make sure
+// the cast is legal!
+// This is the only place in the code we should use dynamic_cast<>.
+// In particular, you SHOULDN'T be using dynamic_cast<> in order to
+// do RTTI (eg code like this:
+// if (dynamic_cast<Subclass1>(foo)) HandleASubclass1Object(foo);
+// if (dynamic_cast<Subclass2>(foo)) HandleASubclass2Object(foo);
+// You should design the code some other way not to need this.
+
+template<typename To, typename From> // use like this: down_cast<T*>(foo);
+inline To down_cast(From* f) { // so we only accept pointers
+ // Ensures that To is a sub-type of From *. This test is here only
+ // for compile-time type checking, and has no overhead in an
+ // optimized build at run-time, as it will be optimized away
+ // completely.
+ if (false) {
+ implicit_cast<From*, To>(0);
+ }
+
+ assert(f == NULL || dynamic_cast<To>(f) != NULL); // RTTI: debug mode only!
+ return static_cast<To>(f);
+}
+
template <class Dest, class Source>
inline Dest bit_cast(const Source& source) {
// Compile time assertion: sizeof(Dest) == sizeof(Source)