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Diffstat (limited to 'runtime/base/casts.h')
-rw-r--r-- | runtime/base/casts.h | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/runtime/base/casts.h b/runtime/base/casts.h new file mode 100644 index 0000000..34c05af --- /dev/null +++ b/runtime/base/casts.h @@ -0,0 +1,93 @@ +/* + * 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 + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +#ifndef ART_SRC_BASE_CASTS_H_ +#define ART_SRC_BASE_CASTS_H_ + +#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 + +#endif // ART_SRC_BASE_CASTS_H_ |