如果std :: greater <>，那么为什么std :: less（而不是std :: lesser <>）？

Question

This apparently looks like a grammatical (and funny?) question but I hope it is not.

I seriously wonder why we have std::greater<> if we don't have std::lesser<> (instead we have std::less<> )? Doesn't it make sense to have either greater and lesser or great and less ? I ask this question because I pretty much mess it up every single time and need to Google it.

Is there some naming convention that the standard follows?

Answer 1

I would say, and this is really just informed speculation, that the authors of the standard made an explicit choice to go one way rather than the other. English, in its near-infinite capacity for confusing people, has many ways for expressing the same idea

a is GREATER than b   =>   a is the GREATER value
a is LESS    than b   =>   a is the LESSER  value

However, since the intent of std::greater and std::less is to return a Boolean value indicating whether the related condition is true, the left-hand column above is the right way to go. If instead it returned the greater or lesser value, it would be more apt to use the right hand column.

In fact, if you look at the ISO standard ( C++11 20.8.5 Comparisons /4 and /5 ), you'll see how they're defined (slightly reformatted):

template <class T> struct greater {
    bool operator()(const T& x, const T& y) const;
    typedef T first_argument_type;
    typedef T second_argument_type;
    typedef bool result_type;
};                                                   // operator() returns x > y.
template <class T> struct less {
    bool operator()(const T& x, const T& y) const;
    typedef T first_argument_type;
    typedef T second_argument_type;
    typedef bool result_type;
};                                                   // operator() returns x < y.

Those comment sections would clearly be read as "returns x is greater than y" and "returns x is less than y".