common/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.
// This file contains macros and macro-like constructs (e.g., templates) that
// are commonly used throughout Chromium source. (It may also contain things
// that are closely related to things that are commonly used that belong in this
// file.)
#pragma once
#include <stddef.h>  // For size_t.

// Put this in the declarations for a class to be uncopyable.
#define DISALLOW_COPY(TypeName) TypeName(const TypeName&) = delete

// Put this in the declarations for a class to be unassignable.
#define DISALLOW_ASSIGN(TypeName) void operator=(const TypeName&) = delete

// A macro to disallow the copy constructor and operator= functions.
// This should be used in the private: declarations for a class.
#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
  TypeName(const TypeName&) = delete;      \
  void operator=(const TypeName&) = delete

// A macro to disallow all the implicit constructors, namely the
// default constructor, copy constructor and operator= functions.
//
// This should be used in the private: declarations for a class
// that wants to prevent anyone from instantiating it. This is
// especially useful for classes containing only static methods.
#define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
  TypeName() = delete;                           \
  DISALLOW_COPY_AND_ASSIGN(TypeName)

// The arraysize(arr) macro returns the # of elements in an array arr.  The
// expression is a compile-time constant, and therefore can be used in defining
// new arrays, for example.  If you use arraysize on a pointer by mistake, you
// will get a compile-time error.  For the technical details, refer to
// http://blogs.msdn.com/b/the1/archive/2004/05/07/128242.aspx.
// This template function declaration is used in defining arraysize.
// Note that the function doesn't need an implementation, as we only
// use its type.
template <typename T, size_t N>
char (&ArraySizeHelper(T (&array)[N]))[N];
#define arraysize(array) (sizeof(ArraySizeHelper(array)))

// 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:
//
//   std::unique_ptr<MyType> my_var = ...;
//   if (TakeOwnership(my_var.get()) == SUCCESS)
//     ignoreResult(my_var.release());
//
template <typename T>
inline void ignoreResult(const T&) {}

template <typename T>
inline void ignoreUnused(T&&) {}