1// Copyright 2014 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// This file contains macros and macro-like constructs (e.g., templates) that
6// are commonly used throughout Chromium source. (It may also contain things
7// that are closely related to things that are commonly used that belong in this
8// file.)
9
10#ifndef BASE_MACROS_H_
11#define BASE_MACROS_H_
12
13#include <stddef.h>  // For size_t.
14
15// Put this in the declarations for a class to be uncopyable.
16#define DISALLOW_COPY(TypeName) \
17  TypeName(const TypeName&) = delete
18
19// Put this in the declarations for a class to be unassignable.
20#define DISALLOW_ASSIGN(TypeName) \
21  void operator=(const TypeName&) = delete
22
23// A macro to disallow the copy constructor and operator= functions
24// This should be used in the private: declarations for a class
25#define DISALLOW_COPY_AND_ASSIGN(TypeName) \
26  TypeName(const TypeName&);               \
27  void operator=(const TypeName&)
28
29// A macro to disallow all the implicit constructors, namely the
30// default constructor, copy constructor and operator= functions.
31//
32// This should be used in the private: declarations for a class
33// that wants to prevent anyone from instantiating it. This is
34// especially useful for classes containing only static methods.
35#define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
36  TypeName() = delete;                           \
37  DISALLOW_COPY_AND_ASSIGN(TypeName)
38
39// The arraysize(arr) macro returns the # of elements in an array arr.  The
40// expression is a compile-time constant, and therefore can be used in defining
41// new arrays, for example.  If you use arraysize on a pointer by mistake, you
42// will get a compile-time error.  For the technical details, refer to
43// http://blogs.msdn.com/b/the1/archive/2004/05/07/128242.aspx.
44
45// This template function declaration is used in defining arraysize.
46// Note that the function doesn't need an implementation, as we only
47// use its type.
48template <typename T, size_t N> char (&ArraySizeHelper(T (&array)[N]))[N];
49#define arraysize(array) (sizeof(ArraySizeHelper(array)))
50
51// Used to explicitly mark the return value of a function as unused. If you are
52// really sure you don't want to do anything with the return value of a function
53// that has been marked WARN_UNUSED_RESULT, wrap it with this. Example:
54//
55//   scoped_ptr<MyType> my_var = ...;
56//   if (TakeOwnership(my_var.get()) == SUCCESS)
57//     ignore_result(my_var.release());
58//
59template<typename T>
60inline void ignore_result(const T&) {
61}
62
63// The following enum should be used only as a constructor argument to indicate
64// that the variable has static storage class, and that the constructor should
65// do nothing to its state.  It indicates to the reader that it is legal to
66// declare a static instance of the class, provided the constructor is given
67// the base::LINKER_INITIALIZED argument.  Normally, it is unsafe to declare a
68// static variable that has a constructor or a destructor because invocation
69// order is undefined.  However, IF the type can be initialized by filling with
70// zeroes (which the loader does for static variables), AND the destructor also
71// does nothing to the storage, AND there are no virtual methods, then a
72// constructor declared as
73//       explicit MyClass(base::LinkerInitialized x) {}
74// and invoked as
75//       static MyClass my_variable_name(base::LINKER_INITIALIZED);
76namespace base {
77enum LinkerInitialized { LINKER_INITIALIZED };
78
79// Use these to declare and define a static local variable (static T;) so that
80// it is leaked so that its destructors are not called at exit. If you need
81// thread-safe initialization, use base/lazy_instance.h instead.
82#define CR_DEFINE_STATIC_LOCAL(type, name, arguments) \
83  static type& name = *new type arguments
84
85}  // base
86
87#endif  // BASE_MACROS_H_
88