c++ - equal_range 如何利用异构比较？

Question

1. 如何触发比较操作Comp{}？std::equal_range是否Comp{}指示正在创建 R 值？

   #include <algorithm>
   #include <vector>
   #include <iostream>
   
    struct S
    {
        int number;
        char name;
        // note: name is ignored by this comparison operator
        bool operator< ( const S& s ) const { return number < s.number; }
    };
   
    int main()
    {
        // note: not ordered, only partitioned w.r.t. S defined below
        const std::vector<S> vec = { {1,'A'}, {2,'B'}, {2,'C'}, {2,'D'}, {4,'G'}, {3,'F'} };
   
        std::cout << "\n" "Using heterogeneous comparison: ";
        struct Comp
        {
            bool operator() ( const S& s, int i ) const { return s.number < i; }
            bool operator() ( int i, const S& s ) const { return i < s.number; }
        };
   
        const auto p2 = std::equal_range(vec.begin(),vec.end(), 2, Comp{});
   
        for ( auto i = p2.first; i != p2.second; ++i )
            std::cout << i->name << ' ';
    }