support remove/erase idiom

[jcageman]

I noticed when applying the remove/erase idiom that the following method is not implemented:

iterator erase ( const_iterator first, const_iterator last );

Reference: https://en.cppreference.com/w/cpp/container/unordered_map/erase
Example:
cache.erase( std::remove_if( cache.begin(), cache.end(), [&] ( const pair<int,int>& i ) { return i.second == 1 ); } ), cache.end() );

[martinus]

This hashmap implementation can't support this use case unfortunately. it = erase(it) works though, so you can at least use the idom that's shown here: https://en.cppreference.com/w/cpp/container/unordered_map/erase

[ed-lam]

I'm using the idiom you mentioned above. On that page, it says:
"The order of the elements that are not erased is preserved. (This makes it possible to erase individual elements while iterating through the container.)".

In other words, I want to erase while iterating the container but never see the same element twice. Is this supported by unordered_flat_map? I'm getting the same element twice.

[martinus]

Hi ed-lam, you shouldn't get the same elements twice. I actually have a test for that in unit_iterators_erase.cpp. Can you submit a short reproducer here? This should work

auto it = map.begin();
while (it != map.end()) {
    it = map.erase(it);
}

[martinus]

Closing until I get a reproducer

[ed-lam]

Here is a minimally working example. It appears the first element is seen again at the end if I delete some elements. This doesn't occur if you change it to std::unordered_map in the example.

robinhood.txt

[martinus]

Thank you for your reproducer! You really stumbled uppon a bug. I could already narrow that bug down to a test case with just two elements. Working on a fix.

[martinus]

Please see #42