Selection.h

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#ifndef CommonTools_Utils_Selection_h
#define CommonTools_Utils_Selection_h
#include <vector>
 
template <typename C, typename Selector, typename StoreContainer = std::vector<const typename C::value_type*> >
class Selection {
public:
  typedef typename C::value_type value_type;
  typedef typename C::size_type size_type;
  typedef value_type& reference;
  typedef const value_type& const_reference;
  Selection(const C& c, const Selector& sel) : select_(sel) {
    for (typename C::const_iterator i = c.begin(); i != c.end(); ++i) {
      if (select_(*i))
        selected_.push_back(&*i);
    }
  }
  class const_iterator {
  public:
    typedef typename Selection<C, Selector, StoreContainer>::value_type value_type;
    typedef value_type* pointer;
    typedef value_type& reference;
    typedef std::ptrdiff_t difference_type;
    typedef typename StoreContainer::const_iterator::iterator_category iterator_category;
    const_iterator(const typename StoreContainer::const_iterator& it) : i(it) {}
    const_iterator(const const_iterator& it) : i(it.i) {}
    const_iterator() {}
    const_iterator& operator=(const const_iterator& it) {
      i = it.i;
      return *this;
    }
    const_iterator& operator++() {
      ++i;
      return *this;
    }
    const_iterator operator++(int) {
      const_iterator ci = *this;
      ++i;
      return ci;
    }
    const_iterator& operator--() {
      --i;
      return *this;
    }
    const_iterator operator--(int) {
      const_iterator ci = *this;
      --i;
      return ci;
    }
    difference_type operator-(const const_iterator& o) const { return i - o.i; }
    const_iterator operator+(difference_type n) const { return const_iterator(i + n); }
    const_iterator operator-(difference_type n) const { return const_iterator(i - n); }
    bool operator<(const const_iterator& o) const { return i < o.i; }
    bool operator==(const const_iterator& ci) const { return i == ci.i; }
    bool operator!=(const const_iterator& ci) const { return i != ci.i; }
    const value_type& operator*() const { return **i; }
    const value_type* operator->() const { return &(operator*()); }
    const_iterator& operator+=(difference_type d) {
      i += d;
      return *this;
    }
    const_iterator& operator-=(difference_type d) {
      i -= d;
      return *this;
    }
 
  private:
    typename StoreContainer::const_iterator i;
  };
  const_iterator begin() const { return const_iterator(selected_.begin()); }
  const_iterator end() const { return const_iterator(selected_.end()); }
  size_type size() const { return selected_.size(); }
  bool empty() const { return selected_.empty(); }
  const_reference operator[](size_type i) { return *selected_[i]; }
 
private:
  Selector select_;
  StoreContainer selected_;
};
 
#endif