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* Copyright (C) 2011 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <assert.h>
#include <string.h>
#include "base/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)
// A compile error here means your Dest and Source have different sizes.
COMPILE_ASSERT(sizeof(Dest) == sizeof(Source), verify_sizes_are_equal);
Dest dest;
memcpy(&dest, &source, sizeof(dest));
return dest;
} // namespace art