From 6ef984af4b0c63c1c33127a12dcfc8e6359f0c9e Mon Sep 17 00:00:00 2001 From: Feng Xiao Date: Mon, 10 Nov 2014 17:34:54 -0800 Subject: Down-integrate from internal code base. --- src/google/protobuf/stubs/casts.h | 123 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 123 insertions(+) create mode 100644 src/google/protobuf/stubs/casts.h (limited to 'src/google/protobuf/stubs/casts.h') diff --git a/src/google/protobuf/stubs/casts.h b/src/google/protobuf/stubs/casts.h new file mode 100644 index 00000000..cccf65a1 --- /dev/null +++ b/src/google/protobuf/stubs/casts.h @@ -0,0 +1,123 @@ +// 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 +#include + +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(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 +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(foo)) HandleASubclass1Object(foo); +// if (dynamic_cast(foo)) HandleASubclass2Object(foo); +// You should design the code some other way not to need this. + +template // use like this: down_cast(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(0); + } + +#if !defined(NDEBUG) && !defined(GOOGLE_PROTOBUF_NO_RTTI) + assert(f == NULL || dynamic_cast(f) != NULL); // RTTI: debug mode only! +#endif + return static_cast(f); +} + +template // use like this: down_cast(foo); +inline To down_cast(From& f) { + typedef typename remove_reference::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(0); + } + +#if !defined(NDEBUG) && !defined(GOOGLE_PROTOBUF_NO_RTTI) + // RTTI: debug mode only! + assert(dynamic_cast(&f) != NULL); +#endif + return *static_cast(&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__ -- cgit v1.2.3