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31_Functor.cpp
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31_Functor.cpp
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// #include <iostream>
// using namespace std;
template <class Arg1, class Arg2, class Result>
struct binary_function {
typedef Arg1 first_argument_type;
typedef Arg2 second_argument_type;
typedef Result result_type;
};
// arithmetic
template <class T>
struct add: public binary_function<T, T, T> {
T operator() (const T& x, const T& y) const { return x+y; }
};
template <class T>
struct subtract: public binary_function<T, T, T> {
T operator() (const T& x, const T& y) const { return x-y; }
};
// logical
template <class T>
struct logical_and: public binary_function<T, T, bool> {
bool operator() (const T& x, const T& y) const { return x && y; }
};
// relational
template <class T>
struct equal_to: public binary_function<T, T, bool> {
bool operator() (const T& x, const T& y) { return x==y; }
};
template <class T>
struct less: public binary_function<T, T, bool> {
bool operator() (const T& x, const T& y) { return x<y; }
};
template <class T>
struct greater: public binary_function<T, T, bool> {
bool operator() (const T& x, const T& y) { return x>y; }
};
template <class Arg, class Result>
struct unary_function {
typedef Arg argument_type;
typedef Result result_type;
};
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 T>
struct identity: public unary_function<T, T> {
const T& operator() (const T& x) const { return x; }
};
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;
}
};