| // 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. | |
| 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 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 == nullptr || dynamic_cast<To>(f) != nullptr); // RTTI: debug mode only! | |
| 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); | |
| } | |
| // RTTI: debug mode only! | |
| assert(dynamic_cast<ToAsPointer>(&f) != nullptr); | |
| 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 | |