type_traits.h

type_traits.h// Filename:    type_traits.h// Comment By:  凝霜// E-mail:      [e-mail]// Blog:        http://blog.csdn.net/mdl13412/* * * Copyright (c) 1997 * Silicon Graphics Computer Systems, Inc. * * Permission to use, copy, modify, distribute and sell this software * and its documentation for any purpose is hereby granted without fee, * provided that the above copyright notice appear in all copies and * that both that copyright notice and this permission notice appear * in supporting documentation.  Silicon Graphics makes no * representations about the suitability of this software for any * purpose.  It is provided "as is" without express or implied warranty. */#ifndef __TYPE_TRAITS_H#define __TYPE_TRAITS_H#ifndef __STL_CONFIG_H#include <stl_config.h>#endif// 这个头文件提供了一个框架, 允许编译器在编译期根据类型属性派发函数的机制// 这个框架对于编写模板代码非常有用// 例如, 当我们需要拷贝一个未知类型的array, 它能帮助我们得知这个未知类型// 是否具有一个trivial copy constructor, 以帮助我们决定memcpy()是否能使用// __type_traits模板类提供了一些列的typedefs, 其值是__true_type或者__false_type// __type_traits模板类可以接受任何类型的参数// 模板类中的typedefs可以通过以下手段获取其正确值//   1. general instantiation, 对于所有类型都要有保守值//   2. 经过特化的版本//   3. 一些编译器(例如Silicon Graphics N32 and N64 compilers)//      会自动给所有类型提供合适的特化版本//// 例子:// Copy an array of elements which have non-trivial copy constructors// template <class T> void copy(T* source,T* destination,int n,__false_type);// Copy an array of elements which have trivial copy constructors. Use memcpy.// template <class T> void copy(T* source,T* destination,int n,__true_type);//// Copy an array of any type by using the most efficient copy mechanism// template <class T> inline void copy(T* source,T* destination,int n)// {//      copy(source,destination,n,//              typename __type_traits<T>::has_trivial_copy_constructor());// }struct __true_type{};struct __false_type{};template <class type>struct __type_traits{    // 不要移除这个成员    // 它通知能自动特化__type_traits的编译器, 现在这个__type_traits template是特化的    // 这是为了确保万一编译器使用了__type_traits而与此处无任何关联的模板时    // 一切也能顺利运作   typedef __true_type     this_dummy_member_must_be_first;   // 以下条款应当被遵守, 因为编译器有可能自动生成类型的特化版本   //   - 你可以重新安排的成员次序   //   - 你可以移除你想移除的成员   //   - 一定不可以修改下列成员名称, 却没有修改编译器中的相应名称   //   - 新加入的成员被当作一般成员, 除非编译器提供特殊支持   typedef __false_type    has_trivial_default_constructor;   typedef __false_type    has_trivial_copy_constructor;   typedef __false_type    has_trivial_assignment_operator;   typedef __false_type    has_trivial_destructor;   typedef __false_type    is_POD_type;};// 以下针对C++内置的基本数据类型提供特化版本, 使其具有trivial default constructor,// copy constructor, assignment operator, destructor// 并标记其为POD类型//// 特化类型://         char, signed char, unsigned char,//         short, unsigned short//         int, unsigned int//         long, unsigned long//         float, double, long double// Provide some specializations.  This is harmless for compilers that//  have built-in __types_traits support, and essential for compilers//  that don't.__STL_TEMPLATE_NULL struct __type_traits<char>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<signed char>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<unsigned char>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<short>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<unsigned short>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<int>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<unsigned int>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<long>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<unsigned long>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<float>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<double>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};__STL_TEMPLATE_NULL struct __type_traits<long double>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION// 针对指针提供特化template <class T>struct __type_traits<T*>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};#else /* __STL_CLASS_PARTIAL_SPECIALIZATION */// 针对char *, signed char *, unsigned char *提供特化struct __type_traits<char*>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};struct __type_traits<signed char*>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};struct __type_traits<unsigned char*>{   typedef __true_type    has_trivial_default_constructor;   typedef __true_type    has_trivial_copy_constructor;   typedef __true_type    has_trivial_assignment_operator;   typedef __true_type    has_trivial_destructor;   typedef __true_type    is_POD_type;};#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */#endif /* __TYPE_TRAITS_H */// Local Variables:// mode:C++// End: