Generic TMP lower_bound_if, upper_bound_if and equal_range_if for any predicates and conditions.

equal_range_if.cpp

template<
	typename Iterator,
	typename Predicate,
	typename Condition
>
Iterator lower_bound_if(Iterator begin,
						Iterator end,
						Predicate predicate,
						Condition condition)
{
	if (begin == end) return end;
	
	auto pivot = begin;
	
	std::advance(pivot, std::distance(begin, end)/2);
	
	if (predicate(*pivot) || condition(*pivot))
	{
		return lower_bound_if(begin, pivot, predicate, condition);
	}
	
	else return lower_bound_if(++pivot, end, predicate, condition);
}

template<
	typename Iterator,
	typename Predicate,
	typename Condition
>
Iterator upper_bound_if(Iterator begin,
						Iterator end,
						Predicate predicate,
						Condition condition)
{
	if (begin == end) return end;
	
	auto pivot = begin;
	
	std::advance(pivot, std::distance(begin, end)/2);
	
	if (! predicate(*pivot) && condition(*pivot))
	{
		return upper_bound_if(begin, pivot, predicate, condition);
	}
	
	else return upper_bound_if(++pivot, end, predicate, condition);
}

template<
	typename Iterator,
	typename Predicate,
	typename Condition
>
std::pair<Iterator, Iterator> equal_range_if(Iterator begin,
											 Iterator end,
											 Predicate predicate,
											 Condition condition)
{
	return {
		lower_bound_if(begin, end, predicate, condition),
		upper_bound_if(begin, end, predicate, condition)
	};
}