decltype.cpp

//
// Created by pengshuai on 2022/4/5.
//


#include <iostream>
#include <vector>
using namespace std;
/**
 * 泛型编程中结合auto，用于追踪函数的返回值类型
 */
template <typename T>

auto multiply(T x, T y) -> decltype(x*y)
{
    return x * y;
}

int main()
{
    int nums[] = {1,2,3,4};
    vector<int> vec(nums,nums+4);
    vector<int>::iterator it;

    for(it = vec.begin(); it != vec.end(); it++)
        cout << *it << " ";
    cout << endl;


    using nullptr_t = decltype(nullptr);
    nullptr_t  nu;
    int *p =NULL;
    if(p == nu)
        cout << "NULL" << endl;


    typedef decltype(vec.begin()) vectype;

    for(vectype i = vec.begin(); i != vec.end(); i++)
        cout << *i << " ";
    cout << endl;

    /**
     * 匿名结构体
     */
    struct
    {
        int d;
        double b;
    } anon_s{};

    decltype(anon_s) as{2, 1}; // 定义了一个上面匿名的结构体
    cout << as.d << endl;

    cout << multiply(11,2) << endl;

    return 0;
}