Implementations of count_until and accumulate_until?

Question

Given an input sequence, the standard algorithms std::count and std::accumulate count the number of occurances of a specific value (or predicate matche

Answer 1

I was thinking of a combination of std::find_if with a state predicate: (Pred is normal user predicate.)

template<class InputIt, class T, class Pred>
typename iterator_traits<InputIterator>::difference_type
count_until(InputIt begin, InputIt end, const T& value, Pred pred)
{
    typename iterator_traits<InputIterator>::difference_type count = 0;
    auto internal_pred = [&count, &value, &pred](decltype(*begin) elem) {
        return elem == value && pred(++count);
    };

    std::find_if(begin, end, internal_pred);
    return count;
}

template<class InputIt, class T, class Pred>
T accumulate_until(InputIt begin, InputIt end, T value, Pred pred)
{
    auto internal_pred = [&value, &pred] (const T& t) {
        value += t;
        return pred(value);
    };
    std::find_if(begin, end, internal_pred);
    return value;
}