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(C++) Negater

A negater is a type of functor that allows to express the opposite of a predicate [1].

Negaters are useful when using algorithms.

Example (using Boost.Bind)

The example below demonstrates how to a find a not-male (that is, a female) using the std::not1 negater.


#include <algorithm>

#include <vector>

#include <boost/bind.hpp>



struct Person

{

  Person(const bool is_male) : m_is_male(is_male) {}

  bool IsMale() const { return m_is_male; }

  const bool m_is_male;

};



bool HasFemale(const std::vector<const Person *>& v)

{

  return std::find_if(

    v.begin(),v.end(),

    std::not1(boost::mem_fn(&Person::IsMale))

    ) != v.end();

}

References

Bjarne Stroustrup. The C++ Programming Language (3rd edition). ISBN: 0-201-88954-4. Chapter 18.4.4: 'A negater allows us to express the opposite of a predicate'

Go back to Richel Bilderbeek's C++ page.

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