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/*
* Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
// Borrowed from Chromium's src/base/macros.h.
#ifndef WEBRTC_SYSTEM_WRAPPERS_INTERFACE_COMPILE_ASSERT_H_
#define WEBRTC_SYSTEM_WRAPPERS_INTERFACE_COMPILE_ASSERT_H_
// The COMPILE_ASSERT macro can be used to verify that a compile time
// expression is true. For example, you could use it to verify the
// size of a static array:
//
// COMPILE_ASSERT(ARRAYSIZE_UNSAFE(content_type_names) == CONTENT_NUM_TYPES,
// content_type_names_incorrect_size);
//
// or to make sure a struct is smaller than a certain size:
//
// COMPILE_ASSERT(sizeof(foo) < 128, foo_too_large);
//
// The second argument to the macro is the name of the variable. If
// the expression is false, most compilers will issue a warning/error
// containing the name of the variable.
// TODO(ajm): Hack to avoid multiple definitions until the base/ of webrtc and
// libjingle are merged.
#if !defined(COMPILE_ASSERT)
#if __cplusplus >= 201103L
// Under C++11, just use static_assert.
#define COMPILE_ASSERT(expr, msg) static_assert(expr, #msg)
#else
template <bool>
struct CompileAssert {
};
#define COMPILE_ASSERT(expr, msg) \
typedef CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1] ALLOW_UNUSED
#endif // __cplusplus >= 201103L
#endif // !defined(COMPILE_ASSERT)
// Implementation details of COMPILE_ASSERT:
//
// - COMPILE_ASSERT works by defining an array type that has -1
// elements (and thus is invalid) when the expression is false.
//
// - The simpler definition
//
// #define COMPILE_ASSERT(expr, msg) typedef char msg[(expr) ? 1 : -1]
//
// does not work, as gcc supports variable-length arrays whose sizes
// are determined at run-time (this is gcc's extension and not part
// of the C++ standard). As a result, gcc fails to reject the
// following code with the simple definition:
//
// int foo;
// COMPILE_ASSERT(foo, msg); // not supposed to compile as foo is
// // not a compile-time constant.
//
// - By using the type CompileAssert<(bool(expr))>, we ensures that
// expr is a compile-time constant. (Template arguments must be
// determined at compile-time.)
//
// - The outer parentheses in CompileAssert<(bool(expr))> are necessary
// to work around a bug in gcc 3.4.4 and 4.0.1. If we had written
//
// CompileAssert<bool(expr)>
//
// instead, these compilers will refuse to compile
//
// COMPILE_ASSERT(5 > 0, some_message);
//
// (They seem to think the ">" in "5 > 0" marks the end of the
// template argument list.)
//
// - The array size is (bool(expr) ? 1 : -1), instead of simply
//
// ((expr) ? 1 : -1).
//
// This is to avoid running into a bug in MS VC 7.1, which
// causes ((0.0) ? 1 : -1) to incorrectly evaluate to 1.
#endif // WEBRTC_SYSTEM_WRAPPERS_INTERFACE_COMPILE_ASSERT_H_
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