mojo/public/c/system/macros.h

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MOJO_PUBLIC_C_SYSTEM_MACROS_H_
#define MOJO_PUBLIC_C_SYSTEM_MACROS_H_

#include <stddef.h>

// Annotate a variable indicating it's okay if it's unused.
// Use like:
//   int x MOJO_ALLOW_UNUSED = ...;
#if defined(__GNUC__)
#define MOJO_ALLOW_UNUSED __attribute__((unused))
#else
#define MOJO_ALLOW_UNUSED
#endif

// Annotate a function indicating that the caller must examine the return value.
// Use like:
//   int foo() MOJO_WARN_UNUSED_RESULT;
// Note that it can only be used on the prototype, and not the definition.
#if defined(__GNUC__)
#define MOJO_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
#else
#define MOJO_WARN_UNUSED_RESULT
#endif

#ifdef __cplusplus
// Used to explicitly mark the return value of a function as unused. If you are
// really sure you don't want to do anything with the return value of a function
// that has been marked WARN_UNUSED_RESULT, wrap it with this. Example:
//
//   scoped_ptr<MyType> my_var = ...;
//   if (TakeOwnership(my_var.get()) == SUCCESS)
//     mojo_ignore_result(my_var.release());
//
template<typename T>
inline void mojo_ignore_result(const T&) {
}
#endif

// Assert things at compile time. (|msg| should be a valid identifier name.)
// This macro is currently C++-only, but we want to use it in the C core.h.
// Use like:
//   MOJO_COMPILE_ASSERT(sizeof(Foo) == 12, Foo_has_invalid_size);
#if __cplusplus >= 201103L
#define MOJO_COMPILE_ASSERT(expr, msg) static_assert(expr, #msg)
#elif defined(__cplusplus)
namespace mojo { template <bool> struct CompileAssert {}; }
#define MOJO_COMPILE_ASSERT(expr, msg) \
    typedef ::mojo::CompileAssert<(bool(expr))> msg[bool(expr) ? 1 : -1]
#else
#define MOJO_COMPILE_ASSERT(expr, msg)
#endif

// Like the C++11 |alignof| operator.
#if __cplusplus >= 201103L
#define MOJO_ALIGNOF(type) alignof(type)
#elif defined(__GNUC__)
#define MOJO_ALIGNOF(type) __alignof__(type)
#elif defined(_MSC_VER)
// The use of |sizeof| is to work around a bug in MSVC 2010 (see
// http://goo.gl/isH0C; supposedly fixed since then).
#define MOJO_ALIGNOF(type) (sizeof(type) - sizeof(type) + __alignof(type))
#else
#error "Please define MOJO_ALIGNOF() for your compiler."
#endif

// Specify the alignment of a |struct|, etc.
// Use like:
//   struct MOJO_ALIGNAS(8) Foo { ... };
// Unlike the C++11 |alignas()|, |alignment| must be an integer. It may not be a
// type, nor can it be an expression like |MOJO_ALIGNOF(type)| (due to the
// non-C++11 MSVS version).
#if __cplusplus >= 201103L
#define MOJO_ALIGNAS(alignment) alignas(alignment)
#elif defined(__GNUC__)
#define MOJO_ALIGNAS(alignment) __attribute__((aligned(alignment)))
#elif defined(_MSC_VER)
#define MOJO_ALIGNAS(alignment) __declspec(align(alignment))
#else
#error "Please define MOJO_ALIGNAS() for your compiler."
#endif

#endif  // MOJO_PUBLIC_C_SYSTEM_MACROS_H_