1/* 2 * libjingle 3 * Copyright 2013, Google Inc. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions are met: 7 * 8 * 1. Redistributions of source code must retain the above copyright notice, 9 * this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright notice, 11 * this list of conditions and the following disclaimer in the documentation 12 * and/or other materials provided with the distribution. 13 * 3. The name of the author may not be used to endorse or promote products 14 * derived from this software without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED 17 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 18 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO 19 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 20 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 21 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 22 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 23 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 24 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 25 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28// COMPILE_ASSERT macro, borrowed from google3/base/macros.h. 29#ifndef TALK_BASE_COMPILE_ASSERT_H_ 30#define TALK_BASE_COMPILE_ASSERT_H_ 31 32// The COMPILE_ASSERT macro can be used to verify that a compile time 33// expression is true. For example, you could use it to verify the 34// size of a static array: 35// 36// COMPILE_ASSERT(ARRAYSIZE(content_type_names) == CONTENT_NUM_TYPES, 37// content_type_names_incorrect_size); 38// 39// or to make sure a struct is smaller than a certain size: 40// 41// COMPILE_ASSERT(sizeof(foo) < 128, foo_too_large); 42// 43// The second argument to the macro is the name of the variable. If 44// the expression is false, most compilers will issue a warning/error 45// containing the name of the variable. 46 47// TODO(ajm): Hack to avoid multiple definitions until the base/ of webrtc and 48// libjingle are merged. 49#if !defined(COMPILE_ASSERT) 50template <bool> 51struct CompileAssert { 52}; 53 54#define COMPILE_ASSERT(expr, msg) \ 55 typedef CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1] // NOLINT 56#endif // COMPILE_ASSERT 57 58// Implementation details of COMPILE_ASSERT: 59// 60// - COMPILE_ASSERT works by defining an array type that has -1 61// elements (and thus is invalid) when the expression is false. 62// 63// - The simpler definition 64// 65// #define COMPILE_ASSERT(expr, msg) typedef char msg[(expr) ? 1 : -1] 66// 67// does not work, as gcc supports variable-length arrays whose sizes 68// are determined at run-time (this is gcc's extension and not part 69// of the C++ standard). As a result, gcc fails to reject the 70// following code with the simple definition: 71// 72// int foo; 73// COMPILE_ASSERT(foo, msg); // not supposed to compile as foo is 74// // not a compile-time constant. 75// 76// - By using the type CompileAssert<(bool(expr))>, we ensures that 77// expr is a compile-time constant. (Template arguments must be 78// determined at compile-time.) 79// 80// - The outer parentheses in CompileAssert<(bool(expr))> are necessary 81// to work around a bug in gcc 3.4.4 and 4.0.1. If we had written 82// 83// CompileAssert<bool(expr)> 84// 85// instead, these compilers will refuse to compile 86// 87// COMPILE_ASSERT(5 > 0, some_message); 88// 89// (They seem to think the ">" in "5 > 0" marks the end of the 90// template argument list.) 91// 92// - The array size is (bool(expr) ? 1 : -1), instead of simply 93// 94// ((expr) ? 1 : -1). 95// 96// This is to avoid running into a bug in MS VC 7.1, which 97// causes ((0.0) ? 1 : -1) to incorrectly evaluate to 1. 98 99#endif // TALK_BASE_COMPILE_ASSERT_H_ 100