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 #if defined(ANDROID)
16 // Prefer Android's libbase definitions to our own.
17 #include <android-base/macros.h>
18 #endif // defined(ANDROID)
19
20 // Put this in the declarations for a class to be uncopyable.
21 #if !defined(DISALLOW_COPY)
22 #define DISALLOW_COPY(TypeName) \
23 TypeName(const TypeName&) = delete
24 #endif
25
26 // Put this in the declarations for a class to be unassignable.
27 #if !defined(DISALLOW_ASSIGN)
28 #define DISALLOW_ASSIGN(TypeName) \
29 void operator=(const TypeName&) = delete
30 #endif
31
32 // A macro to disallow the copy constructor and operator= functions
33 // This should be used in the private: declarations for a class
34 // We define this macro conditionally as it may be defined by another libraries.
35 #if !defined(DISALLOW_COPY_AND_ASSIGN)
36 #define DISALLOW_COPY_AND_ASSIGN(TypeName) \
37 TypeName(const TypeName&) = delete; \
38 void operator=(const TypeName&) = delete
39 #endif
40
41 // A macro to disallow all the implicit constructors, namely the
42 // default constructor, copy constructor and operator= functions.
43 //
44 // This should be used in the private: declarations for a class
45 // that wants to prevent anyone from instantiating it. This is
46 // especially useful for classes containing only static methods.
47 #if !defined(DISALLOW_IMPLICIT_CONSTRUCTORS)
48 #define DISALLOW_IMPLICIT_CONSTRUCTORS(TypeName) \
49 TypeName() = delete; \
50 DISALLOW_COPY_AND_ASSIGN(TypeName)
51 #endif
52
53 // The arraysize(arr) macro returns the # of elements in an array arr. The
54 // expression is a compile-time constant, and therefore can be used in defining
55 // new arrays, for example. If you use arraysize on a pointer by mistake, you
56 // will get a compile-time error. For the technical details, refer to
57 // http://blogs.msdn.com/b/the1/archive/2004/05/07/128242.aspx.
58
59 // This template function declaration is used in defining arraysize.
60 // Note that the function doesn't need an implementation, as we only
61 // use its type.
62 #if !defined(arraysize)
63 template <typename T, size_t N> char (&ArraySizeHelper(T (&array)[N]))[N];
64 #define arraysize(array) (sizeof(ArraySizeHelper(array)))
65 #endif
66
67 // Used to explicitly mark the return value of a function as unused. If you are
68 // really sure you don't want to do anything with the return value of a function
69 // that has been marked WARN_UNUSED_RESULT, wrap it with this. Example:
70 //
71 // std::unique_ptr<MyType> my_var = ...;
72 // if (TakeOwnership(my_var.get()) == SUCCESS)
73 // ignore_result(my_var.release());
74 //
75 template<typename T>
ignore_result(const T &)76 inline void ignore_result(const T&) {
77 }
78
79 // The following enum should be used only as a constructor argument to indicate
80 // that the variable has static storage class, and that the constructor should
81 // do nothing to its state. It indicates to the reader that it is legal to
82 // declare a static instance of the class, provided the constructor is given
83 // the base::LINKER_INITIALIZED argument. Normally, it is unsafe to declare a
84 // static variable that has a constructor or a destructor because invocation
85 // order is undefined. However, IF the type can be initialized by filling with
86 // zeroes (which the loader does for static variables), AND the destructor also
87 // does nothing to the storage, AND there are no virtual methods, then a
88 // constructor declared as
89 // explicit MyClass(base::LinkerInitialized x) {}
90 // and invoked as
91 // static MyClass my_variable_name(base::LINKER_INITIALIZED);
92 namespace base {
93 enum LinkerInitialized { LINKER_INITIALIZED };
94
95 // Use these to declare and define a static local variable (static T;) so that
96 // it is leaked so that its destructors are not called at exit. If you need
97 // thread-safe initialization, use base/lazy_instance.h instead.
98 #if !defined(CR_DEFINE_STATIC_LOCAL)
99 #define CR_DEFINE_STATIC_LOCAL(type, name, arguments) \
100 static type& name = *new type arguments
101 #endif
102
103 } // base
104
105 #endif // BASE_MACROS_H_
106