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iterator_with_predicate
#include <iterator>
#include <functional>
//ForwardIterator Ref.: http://www.cplusplus.com/reference/iterator/ForwardIterator/
template <class Container, class UnaryPredicate>
struct forward_iterator_with_predicate;
template <class Container, class UnaryPredicate>
struct iterator_with_predicate final
{
iterator_with_predicate(Container& cont, UnaryPredicate pred)
: fiwp(cont, pred)
{
refresh();
}
//begin and end:
forward_iterator_with_predicate<Container, UnaryPredicate> begin() const
{
forward_iterator_with_predicate<Container, UnaryPredicate> temp = fiwp;
temp.update_begin();
return temp;
}
forward_iterator_with_predicate<Container, UnaryPredicate> end() const
{
return fiwp;
}
void refresh() { fiwp.update_end(); }
private:
forward_iterator_with_predicate<Container, UnaryPredicate> fiwp;
};
template <class Container, class UnaryPredicate = std::function<bool(typename Container::value_type)>>
auto make_iterator_with_predicate(Container& cont, UnaryPredicate pred) -> iterator_with_predicate<Container, decltype(pred)>
{
return iterator_with_predicate<Container, decltype(pred)>(cont, pred);
}
template <class Container, class UnaryPredicate = std::function<bool(typename Container::value_type)>>
auto begin(iterator_with_predicate<Container, UnaryPredicate>& iwp) -> decltype(iwp.begin())
{
return iwp.begin();
}
template <class Container, class UnaryPredicate>
auto end(iterator_with_predicate<Container, UnaryPredicate> iwp) -> decltype(iwp.end())
{
return iwp.end();
}
template <class Container, class UnaryPredicate>
struct forward_iterator_with_predicate final :
public std::iterator<std::forward_iterator_tag, typename Container::value_type>
{
using value_type = typename Container::value_type;
private:
//constructor and destructor:
explicit forward_iterator_with_predicate(Container& cont, UnaryPredicate pred) :
cont(cont),
pred(pred)
{
}
friend struct iterator_with_predicate<Container, UnaryPredicate>;
public:
//default-constructible
forward_iterator_with_predicate() = delete;
//copy-constructible
forward_iterator_with_predicate(const forward_iterator_with_predicate& that) = default;
//copy-assignable
forward_iterator_with_predicate& operator=(const forward_iterator_with_predicate& that) = default;
~forward_iterator_with_predicate() = default;
//comparison:
//comparable for inequality
bool operator!=(const forward_iterator_with_predicate& that) const
{
return !(*this == that);
}
//comparable for equality
bool operator==(const forward_iterator_with_predicate& that) const
{
return cont_first == that.cont_end;
}
//dereference:
//dereferenceable
value_type& operator*() const
{
return *cont_first;
}
//dereferenceable
value_type* operator->() const
{
return cont_first;
}
//increment:
//pre increment
forward_iterator_with_predicate& operator++()
{
next();
return *this;
}
private:
void update_end()
{
cont_end = cont.end();
}
void update_begin()
{
cont_first = cont.begin();
if (!pred(*cont_first)) //set begin position
next();
}
void next()
{
while (++cont_first != cont_end)
{
if (pred(*cont_first))
break;
}
}
Container& cont;
UnaryPredicate pred;
typename Container::iterator cont_first, cont_end;
};
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