type_traits.h

/*
对不能萃取自定义class是否有trivial default ctor、assignment operator、trivial dtor的大部分编译器
可在本文件中实现该自定义class的__type_traits特化版本。
一个class什么时候会有自己的non-trivial构造析构赋值拷贝函数呢？
当class内存在指针并对它进行动态分配，即会产生浅拷贝问题，所以需要non-trivial-xxx
 */

////////////////////////////////////////////////////////////////////////////////  
/*一个type_traits应用
template <class _ForwardIter, class _Size, class _Tp>
inline _ForwardIter
__uninitialized_fill_n_aux(_ForwardIter __first, _Size __n,
                           const _Tp& __x, __true_type)
{
    return fill_n(__first, __n, __x);
}

template <class _ForwardIter, class _Size, class _Tp>
_ForwardIter
__uninitialized_fill_n_aux(_ForwardIter __first, _Size __n,
                           const _Tp& __x, __false_type)
{
    _ForwardIter __cur = __first;
    __STL_TRY {
        for ( ; __n > 0; --__n, ++__cur)
            _Construct(&*__cur, __x);
        return __cur;
    }
    __STL_UNWIND(_Destroy(__first, __cur));
}

template <class _ForwardIter, class _Size, class _Tp, class _Tp1>
inline _ForwardIter 
__uninitialized_fill_n(_ForwardIter __first, _Size __n, const _Tp& __x, _Tp1*)
{
    typedef typename __type_traits<_Tp1>::is_POD_type _Is_POD;
    return __uninitialized_fill_n_aux(__first, __n, __x, _Is_POD());
}

template <class _ForwardIter, class _Size, class _Tp>
inline _ForwardIter 
uninitialized_fill_n(_ForwardIter __first, _Size __n, const _Tp& __x)
{
    return __uninitialized_fill_n(__first, __n, __x, __VALUE_TYPE(__first));
}
*/
////////////////////////////////////////////////////////////////////////////////  

#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()或memmove()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());  
// }  

//定义struct而非bool用于参数推断
struct __true_type {
};

struct __false_type {
};

template <class _Tp>
struct __type_traits { 
   typedef __true_type     this_dummy_member_must_be_first;
   // 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 

   // 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;
};
//POD :plain   old   data，可以那么理解，就是以前的c语言里面的类型和struct，或者class定义里面单单只是数据，不涉及其他的指针操作，

//也就是说可以通过memcpy拷贝就可以完成复制的


// Provide some specializations.  This is harmless for compilers that
//  have built-in __types_traits support, and essential for compilers
//  that don't.

//对基本类型都提供特化版本，每个成员都是__true_type，所以这些类型都可以用最快速的方式(memcpy,memmove)来拷贝或赋值
#ifndef __STL_NO_BOOL

__STL_TEMPLATE_NULL struct __type_traits<bool> {
   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_NO_BOOL */

__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;
};

#ifdef __STL_HAS_WCHAR_T

__STL_TEMPLATE_NULL struct __type_traits<wchar_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;
};

#endif /* __STL_HAS_WCHAR_T */

__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;
};

#ifdef __STL_LONG_LONG

__STL_TEMPLATE_NULL struct __type_traits<long 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 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;
};

#endif /* __STL_LONG_LONG */

__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

template <class _Tp>
struct __type_traits<_Tp*> {
   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 */

__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<const 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<const 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<const 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 */


// The following could be written in terms of numeric_limits.  
// We're doing it separately to reduce the number of dependencies.
//把所有是整数的类型用特化版本__true_type，否则用__false_type，然后在具体应用中调用重载函数特定版本
template <class _Tp> struct _Is_integer {
  typedef __false_type _Integral;
};

#ifndef __STL_NO_BOOL

__STL_TEMPLATE_NULL struct _Is_integer<bool> {
  typedef __true_type _Integral;
};

#endif /* __STL_NO_BOOL */

__STL_TEMPLATE_NULL struct _Is_integer<char> {
  typedef __true_type _Integral;
};

__STL_TEMPLATE_NULL struct _Is_integer<signed char> {
  typedef __true_type _Integral;
};

__STL_TEMPLATE_NULL struct _Is_integer<unsigned char> {
  typedef __true_type _Integral;
};

#ifdef __STL_HAS_WCHAR_T

__STL_TEMPLATE_NULL struct _Is_integer<wchar_t> {
  typedef __true_type _Integral;
};

#endif /* __STL_HAS_WCHAR_T */

__STL_TEMPLATE_NULL struct _Is_integer<short> {
  typedef __true_type _Integral;
};

__STL_TEMPLATE_NULL struct _Is_integer<unsigned short> {
  typedef __true_type _Integral;
};

__STL_TEMPLATE_NULL struct _Is_integer<int> {
  typedef __true_type _Integral;
};

__STL_TEMPLATE_NULL struct _Is_integer<unsigned int> {
  typedef __true_type _Integral;
};

__STL_TEMPLATE_NULL struct _Is_integer<long> {
  typedef __true_type _Integral;
};

__STL_TEMPLATE_NULL struct _Is_integer<unsigned long> {
  typedef __true_type _Integral;
};

#ifdef __STL_LONG_LONG

__STL_TEMPLATE_NULL struct _Is_integer<long long> {
  typedef __true_type _Integral;
};

__STL_TEMPLATE_NULL struct _Is_integer<unsigned long long> {
  typedef __true_type _Integral;
};

#endif /* __STL_LONG_LONG */

#endif /* __TYPE_TRAITS_H */