function_input_iterator

From: nbecker_at_[hidden]
Date: 2001-05-17 12:46:40

I noticed we have a function_output_iterator, but I didn't see
function_input_iterator.  Here it is.

Example usage:

A function expects to take an iterator as an input.  You want to
provide a constant value.  Use in conjuction with Constant.H:

#ifndef Constant_H
#define Constant_H

#include <functional>

template<typename out_t>
class Constant : public unary_function<out_t, out_t>{
  const out_t val;
public:
  Constant (out_t _val) :
    val (_val) {}

  template<typename T>
  out_t operator() (T x) const {
    return val;
  }

  out_t operator() () const {
    return val;
  }
};

#endif

#ifndef function_input_iterator_hpp
#define function_input_iterator_hpp

#include <iterator>

template <typename UnaryFunction>
class function_input_iterator {
  typedef function_input_iterator self;
public:
  typedef std::input_iterator_tag iterator_category;
  typedef typename UnaryFunction::result_type                value_type;
  typedef void                difference_type;
  typedef void                pointer;
  typedef typename UnaryFunction::result_type&                reference;

  explicit function_input_iterator (const UnaryFunction& f = UnaryFunction()) :
    m_f (f) {}

  value_type operator*() { return m_f(); }
  self& operator++() { return *this; }
  self& operator++(int) { return *this; }
private:
  UnaryFunction m_f;
};

template <typename UnaryFunction>
inline function_input_iterator<UnaryFunction>
make_function_input_iterator(const UnaryFunction& f = UnaryFunction()) {
  return function_input_iterator<UnaryFunction>(f);
}

#endif