C++ STL源码学习（仿函数篇)

stl_function.h

///仿函数的实现并不复杂

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 _Tp>
struct plus : public binary_function<_Tp,_Tp,_Tp>
{
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x + __y;
    }
};

template <class _Tp>
struct minus : public binary_function<_Tp,_Tp,_Tp>
{
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x - __y;
    }
};

template <class _Tp>
struct multiplies : public binary_function<_Tp,_Tp,_Tp>
{
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x * __y;
    }
};

template <class _Tp>
struct divides : public binary_function<_Tp,_Tp,_Tp>
{
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x / __y;
    }
};

/// identity_element (not part of the C++ standard).

template <class _Tp> inline _Tp identity_element(plus<_Tp>)
{
    return _Tp(0);
}
template <class _Tp> inline _Tp identity_element(multiplies<_Tp>)
{
    return _Tp(1);
}

template <class _Tp>
struct modulus : public binary_function<_Tp,_Tp,_Tp>
{
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x % __y;
    }
};

template <class _Tp>
struct negate : public unary_function<_Tp,_Tp>
{
    _Tp operator()(const _Tp& __x) const
    {
        return -__x;
    }
};

template <class _Tp>
struct equal_to : public binary_function<_Tp,_Tp,bool>
{
    bool operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x == __y;
    }
};

template <class _Tp>
struct not_equal_to : public binary_function<_Tp,_Tp,bool>
{
    bool operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x != __y;
    }
};

template <class _Tp>
struct greater : public binary_function<_Tp,_Tp,bool>
{
    bool operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x > __y;
    }
};

template <class _Tp>
struct less : public binary_function<_Tp,_Tp,bool>
{
    bool operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x < __y;
    }
};

template <class _Tp>
struct greater_equal : public binary_function<_Tp,_Tp,bool>
{
    bool operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x >= __y;
    }
};

template <class _Tp>
struct less_equal : public binary_function<_Tp,_Tp,bool>
{
    bool operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x <= __y;
    }
};

template <class _Tp>
struct logical_and : public binary_function<_Tp,_Tp,bool>
{
    bool operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x && __y;
    }
};

template <class _Tp>
struct logical_or : public binary_function<_Tp,_Tp,bool>
{
    bool operator()(const _Tp& __x, const _Tp& __y) const
    {
        return __x || __y;
    }
};

template <class _Tp>
struct logical_not : public unary_function<_Tp,bool>
{
    bool operator()(const _Tp& __x) const
    {
        return !__x;
    }
};

///将传入的函数对象存储,调用该对象的函数调用操作符时,调用
///保存对象的函数调用操作符,并对其返回值求反,再作为该对象
///函数调用操作符的返回值
template <class _Predicate>
class unary_negate
    : public unary_function<typename _Predicate::argument_type, bool>
{
protected:
    _Predicate _M_pred;
public:
    explicit unary_negate(const _Predicate& __x) : _M_pred(__x) {}
    bool operator()(const typename _Predicate::argument_type& __x) const
    {
        return !_M_pred(__x);
    }
};

template <class _Predicate>
inline unary_negate<_Predicate>
not1(const _Predicate& __pred)
{
    return unary_negate<_Predicate>(__pred);
}

template <class _Predicate>
class binary_negate
    : public binary_function<typename _Predicate::first_argument_type,
      typename _Predicate::second_argument_type,
      bool>
{
protected:
    _Predicate _M_pred;
public:
    explicit binary_negate(const _Predicate& __x) : _M_pred(__x) {}
    bool operator()(const typename _Predicate::first_argument_type& __x,
                    const typename _Predicate::second_argument_type& __y) const
    {
        return !_M_pred(__x, __y);
    }
};

template <class _Predicate>
inline binary_negate<_Predicate>
not2(const _Predicate& __pred)
{
    return binary_negate<_Predicate>(__pred);
}

///将传入的函数对象和其第一个参数保存,待需要时,再行绑定
template <class _Operation>
class binder1st
    : public unary_function<typename _Operation::second_argument_type,
      typename _Operation::result_type>
{
protected:
    _Operation op;
    typename _Operation::first_argument_type value;
public:
    binder1st(const _Operation& __x,
              const typename _Operation::first_argument_type& __y)
        : op(__x), value(__y) {}
    typename _Operation::result_type
    operator()(const typename _Operation::second_argument_type& __x) const
    {
        return op(value, __x);
    }
};

template <class _Operation, class _Tp>
inline binder1st<_Operation>
bind1st(const _Operation& __fn, const _Tp& __x)
{
    typedef typename _Operation::first_argument_type _Arg1_type;
    return binder1st<_Operation>(__fn, _Arg1_type(__x));
}

template <class _Operation>
class binder2nd
    : public unary_function<typename _Operation::first_argument_type,
      typename _Operation::result_type>
{
protected:
    _Operation op;
    typename _Operation::second_argument_type value;
public:
    binder2nd(const _Operation& __x,
              const typename _Operation::second_argument_type& __y)
        : op(__x), value(__y) {}
    typename _Operation::result_type
    operator()(const typename _Operation::first_argument_type& __x) const
    {
        return op(__x, value);
    }
};

template <class _Operation, class _Tp>
inline binder2nd<_Operation>
bind2nd(const _Operation& __fn, const _Tp& __x)
{
    typedef typename _Operation::second_argument_type _Arg2_type;
    return binder2nd<_Operation>(__fn, _Arg2_type(__x));
}

/// unary_compose and binary_compose (extensions, not part of the standard).
///将两个医院函数组合为一个一元参数,第二个函数的返回值作为第一个函数的参数
template <class _Operation1, class _Operation2>
class unary_compose
    : public unary_function<typename _Operation2::argument_type,
      typename _Operation1::result_type>
{
protected:
    _Operation1 _M_fn1;
    _Operation2 _M_fn2;
public:
    unary_compose(const _Operation1& __x, const _Operation2& __y)
        : _M_fn1(__x), _M_fn2(__y) {}
    typename _Operation1::result_type
    operator()(const typename _Operation2::argument_type& __x) const
    {
        return _M_fn1(_M_fn2(__x));
    }
};

template <class _Operation1, class _Operation2>
inline unary_compose<_Operation1,_Operation2>
compose1(const _Operation1& __fn1, const _Operation2& __fn2)
{
    return unary_compose<_Operation1,_Operation2>(__fn1, __fn2);
}

template <class _Operation1, class _Operation2, class _Operation3>
class binary_compose
    : public unary_function<typename _Operation2::argument_type,
      typename _Operation1::result_type>
{
protected:
    _Operation1 _M_fn1;
    _Operation2 _M_fn2;
    _Operation3 _M_fn3;
public:
    binary_compose(const _Operation1& __x, const _Operation2& __y,
                   const _Operation3& __z)
        : _M_fn1(__x), _M_fn2(__y), _M_fn3(__z) { }
    typename _Operation1::result_type
    operator()(const typename _Operation2::argument_type& __x) const
    {
        return _M_fn1(_M_fn2(__x), _M_fn3(__x));
    }
};

template <class _Operation1, class _Operation2, class _Operation3>
inline binary_compose<_Operation1, _Operation2, _Operation3>
compose2(const _Operation1& __fn1, const _Operation2& __fn2,
         const _Operation3& __fn3)
{
    return binary_compose<_Operation1,_Operation2,_Operation3>
           (__fn1, __fn2, __fn3);
}

template <class _Arg, class _Result>
class pointer_to_unary_function : public unary_function<_Arg, _Result>
{
protected:
///返回值为_Result类型,参数类型为_Arg的函数指针
    _Result (*_M_ptr)(_Arg);
public:
    pointer_to_unary_function() {}
    explicit pointer_to_unary_function(_Result (*__x)(_Arg)) : _M_ptr(__x) {}
    _Result operator()(_Arg __x) const
    {
        return _M_ptr(__x);
    }
};

template <class _Arg, class _Result>
inline pointer_to_unary_function<_Arg, _Result> ptr_fun(_Result (*__x)(_Arg))
{
    return pointer_to_unary_function<_Arg, _Result>(__x);
}

template <class _Arg1, class _Arg2, class _Result>
class pointer_to_binary_function :
    public binary_function<_Arg1,_Arg2,_Result>
{
protected:
    _Result (*_M_ptr)(_Arg1, _Arg2);
public:
    pointer_to_binary_function() {}
    explicit pointer_to_binary_function(_Result (*__x)(_Arg1, _Arg2))
        : _M_ptr(__x) {}
    _Result operator()(_Arg1 __x, _Arg2 __y) const
    {
        return _M_ptr(__x, __y);
    }
};

template <class _Arg1, class _Arg2, class _Result>
inline pointer_to_binary_function<_Arg1,_Arg2,_Result>
ptr_fun(_Result (*__x)(_Arg1, _Arg2))
{
    return pointer_to_binary_function<_Arg1,_Arg2,_Result>(__x);
}

/// identity is an extensions: it is not part of the standard.
template <class _Tp>
struct _Identity : public unary_function<_Tp,_Tp>
{
    const _Tp& operator()(const _Tp& __x) const
    {
        return __x;
    }
};

template <class _Tp> struct identity : public _Identity<_Tp> {};

/// select1st and select2nd are extensions: they are not part of the standard.

///_Select1st和_Select2nd为了在map和multimap中作为根据值推导键的函数来提供的
///除此之外,STL中未用到
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;
    }
};

template <class _Pair> struct select1st : public _Select1st<_Pair> {};
template <class _Pair> struct select2nd : public _Select2nd<_Pair> {};

///由于成员函数的调用,隐式传递了一个this指针,因此只需要将这个this指针
///变成显式传递,即可当做普通函数使用,STL成员函数适配器即采用这种方法

///将_Tp类的对象指针和其返回值为_Ret,参数为空的成员函数绑定,生成
///一个一元函数,该一元函数的参数为_Tp类指针
template <class _Ret, class _Tp>
class mem_fun_t : public unary_function<_Tp*,_Ret>
{
public:
    explicit mem_fun_t(_Ret (_Tp::*__pf)()) : _M_f(__pf) {}
    _Ret operator()(_Tp* __p) const
    {
        return (__p->*_M_f)();
    }
private:
    _Ret (_Tp::*_M_f)();
};

///将_Tp类的对象指针和其返回值为_Ret,参数为空的常成员函数绑定,生成
///一个一元函数,该一元函数的参数为指向const Tp 类的指针
template <class _Ret, class _Tp>
class const_mem_fun_t : public unary_function<const _Tp*,_Ret>
{
public:
    explicit const_mem_fun_t(_Ret (_Tp::*__pf)() const) : _M_f(__pf) {}
    _Ret operator()(const _Tp* __p) const
    {
        return (__p->*_M_f)();
    }
private:
    _Ret (_Tp::*_M_f)() const;
};

///将_Tp类的对象和其返回值为_Ret,参数为空的成员函数绑定,生成
///一个一元函数
template <class _Ret, class _Tp>
class mem_fun_ref_t : public unary_function<_Tp,_Ret>
{
public:
    explicit mem_fun_ref_t(_Ret (_Tp::*__pf)()) : _M_f(__pf) {}
    _Ret operator()(_Tp& __r) const
    {
        return (__r.*_M_f)();
    }
private:
    _Ret (_Tp::*_M_f)();
};

///将_Tp类的对象和其返回值为_Ret,参数为空的常成员函数绑定,生成
///一个一元函数
template <class _Ret, class _Tp>
class const_mem_fun_ref_t : public unary_function<_Tp,_Ret>
{
public:
    explicit const_mem_fun_ref_t(_Ret (_Tp::*__pf)() const) : _M_f(__pf) {}
    _Ret operator()(const _Tp& __r) const
    {
        return (__r.*_M_f)();
    }
private:
    _Ret (_Tp::*_M_f)() const;
};

///将_Tp类的对象和其返回值为_Ret,参数为_Arg类型的常成员函数绑定,生成
///一个二元函数
template <class _Ret, class _Tp, class _Arg>
class mem_fun1_t : public binary_function<_Tp*,_Arg,_Ret>
{
public:
    explicit mem_fun1_t(_Ret (_Tp::*__pf)(_Arg)) : _M_f(__pf) {}
    _Ret operator()(_Tp* __p, _Arg __x) const
    {
        return (__p->*_M_f)(__x);
    }
private:
    _Ret (_Tp::*_M_f)(_Arg);
};

template <class _Ret, class _Tp, class _Arg>
class const_mem_fun1_t : public binary_function<const _Tp*,_Arg,_Ret>
{
public:
    explicit const_mem_fun1_t(_Ret (_Tp::*__pf)(_Arg) const) : _M_f(__pf) {}
    _Ret operator()(const _Tp* __p, _Arg __x) const
    {
        return (__p->*_M_f)(__x);
    }
private:
    _Ret (_Tp::*_M_f)(_Arg) const;
};

template <class _Ret, class _Tp, class _Arg>
class mem_fun1_ref_t : public binary_function<_Tp,_Arg,_Ret>
{
public:
    explicit mem_fun1_ref_t(_Ret (_Tp::*__pf)(_Arg)) : _M_f(__pf) {}
    _Ret operator()(_Tp& __r, _Arg __x) const
    {
        return (__r.*_M_f)(__x);
    }
private:
    _Ret (_Tp::*_M_f)(_Arg);
};

template <class _Ret, class _Tp, class _Arg>
class const_mem_fun1_ref_t : public binary_function<_Tp,_Arg,_Ret>
{
public:
    explicit const_mem_fun1_ref_t(_Ret (_Tp::*__pf)(_Arg) const) : _M_f(__pf) {}
    _Ret operator()(const _Tp& __r, _Arg __x) const
    {
        return (__r.*_M_f)(__x);
    }
private:
    _Ret (_Tp::*_M_f)(_Arg) const;
};

template <class _Ret, class _Tp>
inline mem_fun_t<_Ret,_Tp> mem_fun(_Ret (_Tp::*__f)())
{
    return mem_fun_t<_Ret,_Tp>(__f);
}

template <class _Ret, class _Tp>
inline const_mem_fun_t<_Ret,_Tp> mem_fun(_Ret (_Tp::*__f)() const)
{
    return const_mem_fun_t<_Ret,_Tp>(__f);
}

template <class _Ret, class _Tp>
inline mem_fun_ref_t<_Ret,_Tp> mem_fun_ref(_Ret (_Tp::*__f)())
{
    return mem_fun_ref_t<_Ret,_Tp>(__f);
}

template <class _Ret, class _Tp>
inline const_mem_fun_ref_t<_Ret,_Tp> mem_fun_ref(_Ret (_Tp::*__f)() const)
{
    return const_mem_fun_ref_t<_Ret,_Tp>(__f);
}

template <class _Ret, class _Tp, class _Arg>
inline mem_fun1_t<_Ret,_Tp,_Arg> mem_fun(_Ret (_Tp::*__f)(_Arg))
{
    return mem_fun1_t<_Ret,_Tp,_Arg>(__f);
}

template <class _Ret, class _Tp, class _Arg>
inline const_mem_fun1_t<_Ret,_Tp,_Arg> mem_fun(_Ret (_Tp::*__f)(_Arg) const)
{
    return const_mem_fun1_t<_Ret,_Tp,_Arg>(__f);
}

template <class _Ret, class _Tp, class _Arg>
inline mem_fun1_ref_t<_Ret,_Tp,_Arg> mem_fun_ref(_Ret (_Tp::*__f)(_Arg))
{
    return mem_fun1_ref_t<_Ret,_Tp,_Arg>(__f);
}

template <class _Ret, class _Tp, class _Arg>
inline const_mem_fun1_ref_t<_Ret,_Tp,_Arg>
mem_fun_ref(_Ret (_Tp::*__f)(_Arg) const)
{
    return const_mem_fun1_ref_t<_Ret,_Tp,_Arg>(__f);
}

template <class _Ret, class _Tp, class _Arg>
inline mem_fun1_t<_Ret,_Tp,_Arg> mem_fun1(_Ret (_Tp::*__f)(_Arg))
{
    return mem_fun1_t<_Ret,_Tp,_Arg>(__f);
}

template <class _Ret, class _Tp, class _Arg>
inline const_mem_fun1_t<_Ret,_Tp,_Arg> mem_fun1(_Ret (_Tp::*__f)(_Arg) const)
{
    return const_mem_fun1_t<_Ret,_Tp,_Arg>(__f);
}

template <class _Ret, class _Tp, class _Arg>
inline mem_fun1_ref_t<_Ret,_Tp,_Arg> mem_fun1_ref(_Ret (_Tp::*__f)(_Arg))
{
    return mem_fun1_ref_t<_Ret,_Tp,_Arg>(__f);
}

template <class _Ret, class _Tp, class _Arg>
inline const_mem_fun1_ref_t<_Ret,_Tp,_Arg>
mem_fun1_ref(_Ret (_Tp::*__f)(_Arg) const)
{
    return const_mem_fun1_ref_t<_Ret,_Tp,_Arg>(__f);
}