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