Return removed element count in erase and erase_if #75
Description
Disclaimer: if it's not the place to post this type of suggestions, please redirect me to the correct one.
In my opinion, erase and erase_if algorithms added by this TS should return the number of removed elements instead of void.
For instance, std::list::remove and std::list::remove_if (https://en.cppreference.com/w/cpp/container/list/remove) return this count since C++20.
I may be mistaken, but I see no substantial overhead to returnig removed count in erase and erase_if.
For lists and forward_lists, just return c.remove_if(pred); is enough.
For maps, storing old size before the removal, and returning .size() - old_size would be enough.
For vectors and deques, the overhead is minimal and consists in calling std::distance with the iterator resulting from the call to std::remove_if before calling c.erase(...).
I.e. for vectors and deques, it would look like:
template <typename Container, typename Pred>
std::size_t erase_remove_if(Container & c, Pred pred)
{
const auto last = std::end(c);
auto new_last = std::remove_if(std::begin(c), last, pred);
const auto removed_count = std::distance(new_last, last);
c.erase(new_last, last);
return removed_count;
}and for node-based containers:
template <typename Container, typename Pred>
std::size_t erase_nodes_if(Container & c, Pred pred)
{
const std::size_t old_size = std::size(c);
auto it = c.begin();
const auto last = c.end();
while (it != last)
{
if (pred(*it))
{
it = c.erase(it);
assert(last == c.end());
}
else
{
++it;
}
}
return old_size - std::size(c);
}