myFunction.h

#ifndef _MYFUNCTION_H
#define _MYFUNCTION_H
namespace mySTL {
    template <class T1, class T2>
    struct pair {
        typedef T1 first_type;
        typedef T2 second_type;
        T1 first;
        T2 second;
        pair() : first(T1()), second(T2()) {}
        pair(const T1& a, const T2&b) : first(a), second(b) {}
    };
    
    template <class Arg, class Result>
    struct unary_function {
        typedef Arg argument_type;
        typedef Result result_type;
    };
    template <class Arg1, class Arg2, class Result>
    struct binary_function {
        typedef Arg1 first_argument_type;
        typedef Arg2 second_argument_type;
        typedef Result result_type;
    };
    
    template <class T>
    struct identity : public unary_function<T, T> {
        const T& operator() (const T& x) const { return x; }
    };

    template <class T>
    struct less : public binary_function<T, T, bool> {
        bool operator() (const T& x, const T& y) const { return x < y; }
    };

    template <class T>
    struct greater : public binary_function<T, T, bool> {
        bool operator() (const T& x, const T& y) const { return x > y; }
    };

    //选择函数
    template <class Pair>
    struct select1st : public unary_function<Pair, typename Pair::first_type> {
        const typename Pair::first_type& operator() (const Pair& x) const { return x.first; }
    };
    template <class Pair>
    struct select2nd : public unary_function<Pair, typename Pair::second_type> {
        const typename Pair::second_type& operator() (const Pair& x) const { return x.second; }
    };
}
#endif