《探索现代化C++》泛读笔记摘要19

Chapter 元编程

提供和使用类型信息

主要的头文件 <type_traits> 和 <limits>

Type Traits

C++11

#include <iostream>
#include <complex>
#include <vector>
 
using namespace std;
 
template<typename T>
struct Magnitude
{
    using type = T;
};
 
// 偏特化
template<typename T>
struct Magnitude<std::complex<T>>
{
    using type = T;
};
 
template<typename T>
struct Magnitude<vector<T>>
{
    using type = typename Magnitude<T>::type;
};
 
template<typename T>
T inline min_magnitude(const T& x, const T& y)
{
    using std::abs;
    typename Magnitude<T>::type ax = abs(x), ay = abs(y);
    return ax < ay ? x : y;
}
 
int main()
{
    double d1 = 3., d2 = 4.;
    cout << "min |d1, d2| = " << min_magnitude(d1, d2) << '\n';
    std::complex<double> c1(3.), c2(4.);
    cout << "min |c1, c2| = " << min_magnitude(c1, c2) << '\n';
}

C++11 条件异常处理

#include <type_traits>
 
template <typename T>
inline T clone(const T& x)
noexcept(std::is_nothrow_copy_constructible<T>::value)
{
    return T{ x };
}