#include <algorithm>
#include <compare>
#include <vector>
#include <iostream>
 
struct S
{
    int number;
    char name;
    // 注：这些比较运算符忽略名称
    friend bool operator==  ( const S s1, const S s2 ) { return s1.number == s2.number; }
    friend auto operator<=> ( const S s1, const S s2 ) { return s1.number <=> s2.number; }
};
 
int main()
{
    // 注：非有序，仅按照定义如下的 S 划分
    std::vector<S> vec = { {1,'A'}, {2,'B'}, {2,'C'}, {2,'D'}, {4, 'D'}, {4,'G'}, {3,'F'} };
 
    S value = {2, '?'};
 
    namespace ranges = std::ranges;
 
    {
        auto p = ranges::equal_range(vec, value);
 
        for ( auto i : p )
            std::cout << i.name << ' ';
    }
    {
        auto p = ranges::equal_range(vec.begin(), vec.end(), value);
 
        for ( auto i = p.begin(); i != p.end(); ++i )
            std::cout << i->name << ' ';
    }
 
    std::cout << '\n';
 
    {
        auto p = ranges::equal_range(vec, 'D', ranges::less{}, &S::name);
 
        for ( auto i : p )
            std::cout << i.name << ' ';
    }
    {
        auto p = ranges::equal_range(vec.begin(),vec.end(), 'D', ranges::less{}, &S::name);
 
        for ( auto i = p.begin(); i != p.end(); ++i )
            std::cout << i->name << ' ';
    }
}