类型萃取器__type_traits

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#struct #class

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本文介绍了一个模板特化的高效方法，用于快速检查C++中基本数据类型的特有属性，如默认构造函数、复制构造函数、赋值运算符和析构函数的特性，并判断它们是否为POD类型。

//type_traits.h
#ifndef TYPE_TRAITS_H
#define TYPE_TRAITS_H

struct __true_type {};
struct __false_type {};

template <typename type>
struct __type_traits {
	//不要移除
	typedef __true_type this_dummy_member_must_be_first;

	//trivial指无意义的
	typedef __false_type has_trivial_default_constructor;
	typedef __false_type has_trivial_copy_constructor;
	typedef __false_type has_trivial_assignment_constructor;
	typedef __false_type has_trivial_destructor;
	typedef __false_type is_POD_type;
	//POD指的是这样一些数据类型：基本数据类型、指针、union、数组、
	//构造函数是 trivial 的 struct 或者 class
};

//特化版本
template <>
struct __type_traits<char> {
	typedef __true_type has_trivial_default_constructor;
	typedef __true_type has_trivial_copy_constructor;
	typedef __true_type has_trivial_assignment_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
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_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
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_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
struct __type_traits<short> {
	typedef __true_type has_trivial_default_constructor;
	typedef __true_type has_trivial_copy_constructor;
	typedef __true_type has_trivial_assignment_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
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_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
struct __type_traits<int> {
	typedef __true_type has_trivial_default_constructor;
	typedef __true_type has_trivial_copy_constructor;
	typedef __true_type has_trivial_assignment_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
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_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
struct __type_traits<long> {
	typedef __true_type has_trivial_default_constructor;
	typedef __true_type has_trivial_copy_constructor;
	typedef __true_type has_trivial_assignment_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
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_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
struct __type_traits<float> {
	typedef __true_type has_trivial_default_constructor;
	typedef __true_type has_trivial_copy_constructor;
	typedef __true_type has_trivial_assignment_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
struct __type_traits<double> {
	typedef __true_type has_trivial_default_constructor;
	typedef __true_type has_trivial_copy_constructor;
	typedef __true_type has_trivial_assignment_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本
template <>
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_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};
//特化版本(原生指针)
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_constructor;
	typedef __true_type has_trivial_destructor;
	typedef __true_type is_POD_type;
};

#endif