Legibilidade com C++14 - get_numeric

numeric.cpp

template<class OutputIterator, class ValueType>
struct numerical_appender {
	numerical_appender(OutputIterator it) : _it(it) { }
	void operator()(const ValueType c) {
		if( c >= '0' && c <= '9' ) {
			*_it = c;
			_it++;
		}
	}
private:
	OutputIterator _it;
};

template<class T>
void get_numeric(const T &input, T &output) 
{
	typedef std::back_insert_iterator<T> it_type;
	it_type it = std::back_inserter(output);
	numerical_appender<it_type, typename T::value_type> appender(it);
	std::for_each(input.begin(), input.end(), appender);
}