c++ - map 在运行时选择 `std::greater` 或 `std::less`

Question

这一行:

std::map<long int, long int, std::greater<long int>> current_book;

我想用以下逻辑等价物替换它:

int Side = ...
if (Side == 1){
    std::map<long int, long int, std::greater<long int>> current_book;
} else {
    std::map<long int, long int, std::less<long int>> current_book;
}

Answer 1

您可以为此使用 std::function:

using mymap = std::map<long,long,std::function<bool(long,long)>>;
auto m = Side ? mymap( std::less<long>() ) : mymap( std::greater<long>() );

live example