最近看了《STL源码剖析》和侯捷老师的STL课程，打算做一个小型的STL，在增加项目经验的同时也顺带复习STL和数据结构相关的知识。整个系列完全参考岚岚路的博客和github上的一个STL项目项目地址

任务

STL中有多种形形色色的Traits，其中type_traits负责萃取类型特性，即某种类型是否具有琐碎无意义（trivial）的构造函数或复制控制，即POD类型（Plain Old Data）。

#ifndef  _TYPE_TRAITS_H_
#define _TYPE_TRAITS_H_
namespace mySTL {
    
    
	namespace {
    
    
		template<bool, class  Ta,class Tb>
		struct IfThenElse;
		template<class Ta,class Tb>
		struct IfThenElse<true, Ta, Tb>
		{
    
    
			using result = Ta;
		};
		template<class Ta, class Tb>
		struct IfThenElse<false, Ta, Tb>
		{
    
    
			using result = Tb;
		};
	}
}
struct _true_type{
    
    };
struct _false_type{
    
    };
//萃取传入的T类型的类型特性
template<class T>
struct _type_traits
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<bool>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<char>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<unsigned char>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<signed char>//在32位系统中一个char类型一般为8个bit，所以能存储的数据范围为-128~127，而unsigned char则是0~255，存储范围相同
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<wchar_t>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<short>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<unsigned short>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<int>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<unsigned int>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<long>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<unsigned long>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<long long>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<unsigned long long>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<double>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits< long double>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<class T>
struct _type_traits< T*>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<class T>
struct _type_traits<const T*>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits< char *>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<const char *>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<const unsigned char *>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
template<>
struct _type_traits<const signed char *>
{
    
    
	typedef _false_type has_trivial_default_constructor;
	typedef _false_type has_trivial_copy_constructor;
	typedef _false_type has_trivial_assaignment_operator;
	typedef _false_type has_trivial_destructor;
	typedef _false_type is_POD_type;
};
#endif // ! _TYPE_TRAITS_H_