| // Protocol Buffers - Google's data interchange format |
| // Copyright 2014 Google Inc. All rights reserved. |
| // https://developers.google.com/protocol-buffers/ |
| // |
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| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
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| // 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. |
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| // 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 |
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| // 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/stubs/type_traits.h> |
| |
| 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); |
| } |
| |
| #if !defined(NDEBUG) && !defined(GOOGLE_PROTOBUF_NO_RTTI) |
| assert(f == NULL || dynamic_cast<To>(f) != NULL); // 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 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) && !defined(GOOGLE_PROTOBUF_NO_RTTI) |
| // RTTI: debug mode only! |
| assert(dynamic_cast<ToAsPointer>(&f) != NULL); |
| #endif |
| return *static_cast<ToAsPointer>(&f); |
| } |
| |
| } // 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; |
| |
| } // namespace protobuf |
| } // namespace google |
| #endif // GOOGLE_PROTOBUF_CASTS_H__ |