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. 48 template <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 // 59 template<typename T> 60 inline 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); 76 namespace base { 77 enum 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
