Down-integrate from internal code base.

1 files changed, 123 insertions, 0 deletions

diff --git a/src/google/protobuf/stubs/casts.h b/src/google/protobuf/stubs/casts.h
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+++ b/src/google/protobuf/stubs/casts.h
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+// 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/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__