C++泛型 重载 ＜＜

#ifndef VECTOR_OPS_FOR_NN
#define VECTOR_OPS_FOR_NN

#include <algorithm>
#include <chrono>
#include <iostream>
#include <random>
#include <valarray>
#include <vector>

namespace machine_learning{
    
    
    // 重载<< 打印二维数组
    template <typename T>
    std::ostream &operator<<(std::ostream &out, std::vector<std::valarray<T>> const &A){
    
    
        out.precision(4);   // 取数据的前四位有效数字
        for(const auto &a : A){
    
    
            for(const auto &x : a){
    
    
                std::cout << x << ' ';
            }
            std::cout << std::endl;
        }
        return out;
    }

    // 重载 << 打印pair
    template <typename T>
    std::ostream &operator <<(std::ostream &out, const std::pair<T,T> &A){
    
    
        out.precision(4);
        // printing pair in the form (p, q)
        std::cout << "(" << A.first << ", " << A.second << ")";
        return out;
    }

    // 重载<< 打印一维数组
    template <typename T>
    std::ostream &operator<<(std::ostream &out, std::vector<T> const &A){
    
    
        out.precision(4);
        for(const auto &a : A){
    
    
            std::cout << a << ' ';
        }
        std::cout << std::endl;
        return out;
    }

    template <typename T>
    std::ostream &operator<<(std::ostream &out, std::valarray<T> const &A){
    
    
        out.precision(4);
        for(const auto &a : A){
    
    
            std::cout << a << ' ';
        }
        std::cout << std::endl;
        return out;
    }

    // 将element插入1D vector
    template <typename T>
    std::valarray<T> insert_element(const std::valarray<T> &A, const T &ele){
    
    
        std::valarray<T> B;     // 存储新的1D
        B.resize(A.size() + 1); // 调整大小
        for (size_t i = 0; i < A.size(); i++){
    
    
            B[i] = A[i];
        }
        B[B.size() - 1] = ele;  // 最后位置插入新元素
        return B;
    }


    void test01(){
    
    


        // print 1D vector
        std::vector<int> weekdays;
        weekdays.push_back(2);
        weekdays.push_back(3);
        weekdays.push_back(4);
        weekdays.push_back(5);
        std::cout << "print 1D vector: " << weekdays;

        // insert element
        // 创建一个大小为4、值全为3的valarray
        std::valarray<int> valarray_A(3, 4);
        int a = 5;
        std::valarray<int> B = insert_element(valarray_A, a);
        std::cout << "insert_element: " << B << std::endl;

        // print vector<std::valarray<int>>
        std::vector<std::valarray<int>> vec_va;
        vec_va.push_back(B);
        vec_va.push_back(B);
        std::cout << "print vector<std::valarray<int>>: " << vec_va << std::endl;

        // print pair
        std::pair<int, int> pair_A = {
    
    1, 2};
        std::cout << "print pair = "<< pair_A << std::endl;
    }
}
#endif

int main(){
    
    
    machine_learning::test01();
}

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