How do I call a templatized operator()()?

问题

I have a struct that looks something like:

struct foo_t
{
    template <std::size_t x, std::size_t y>
    std::size_t operator()() const
    { return /*something dealing with x and y*/; }
};

The definition seems to compile fine, but how do I call it? I can't seem to get anything past the compiler:

foo_t foo;
foo<3, 3>(); // ERROR: Compiler seems to think I'm asking for "foo < 3 ..."

回答1:

It's ugly, but..,

foo_t foo;
foo.operator()<3, 3>();

_{Online demo.}

来源：https://stackoverflow.com/questions/11105060/how-do-i-call-a-templatized-operator