// Protocol Buffers - Google's data interchange format // Copyright 2014 Google Inc. All rights reserved. // https://developers.google.com/protocol-buffers/ // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above // copyright notice, this list of conditions and the following disclaimer // in the documentation and/or other materials provided with the // distribution. // * Neither the name of Google Inc. nor the names of its // contributors may be used to endorse or promote products derived from // this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. #ifndef GOOGLE_PROTOBUF_CASTS_H__ #define GOOGLE_PROTOBUF_CASTS_H__ #include <google/protobuf/stubs/common.h> #include <google/protobuf/port_def.inc> #include <type_traits> namespace google { namespace protobuf { namespace internal { // 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 convertible 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); } #if !defined(NDEBUG) && PROTOBUF_RTTI assert(f == nullptr || dynamic_cast<To>(f) != nullptr); // RTTI: debug mode only! #endif return static_cast<To>(f); } template<typename To, typename From> // use like this: down_cast<T&>(foo); inline To down_cast(From& f) { typedef typename std::remove_reference<To>::type* ToAsPointer; // 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*, ToAsPointer>(0); } #if !defined(NDEBUG) && PROTOBUF_RTTI // RTTI: debug mode only! assert(dynamic_cast<ToAsPointer>(&f) != nullptr); #endif return *static_cast<ToAsPointer>(&f); } template<typename To, typename From> inline To bit_cast(const From& from) { GOOGLE_COMPILE_ASSERT(sizeof(From) == sizeof(To), bit_cast_with_different_sizes); To dest; memcpy(&dest, &from, sizeof(dest)); return dest; } } // namespace internal // We made these internal so that they would show up as such in the docs, // but we don't want to stick "internal::" in front of them everywhere. using internal::implicit_cast; using internal::down_cast; using internal::bit_cast; } // namespace protobuf } // namespace google #include <google/protobuf/port_undef.inc> #endif // GOOGLE_PROTOBUF_CASTS_H__