protected override async ValueTask <bool> MoveNextCore()
{
// NB: Earlier implementations of this operator constructed the set for the second source concurrently
// with the first MoveNextAsync call on the first source. This resulted in an unexpected source of
// concurrency, which isn't a great default behavior because it's very hard to suppress or control
// this behavior.
switch (_state)
{
case AsyncIteratorState.Allocated:
_set = await AsyncEnumerableHelpers.ToSet(_second, _comparer, _cancellationToken).ConfigureAwait(false);
_firstEnumerator = _first.GetAsyncEnumerator(_cancellationToken);
_state = AsyncIteratorState.Iterating;
goto case AsyncIteratorState.Iterating;
case AsyncIteratorState.Iterating:
bool moveNext;
do
{
moveNext = await _firstEnumerator.MoveNextAsync().ConfigureAwait(false);
if (moveNext)
{
var item = _firstEnumerator.Current;
if (_set.Remove(item))
{
_current = item;
return(true);
}
}
} while (moveNext);
await DisposeAsync().ConfigureAwait(false);
break;
}
return(false);
}
private Task <Set <TSource> > FillSetAsync(CancellationToken cancellationToken)
{
return(AsyncEnumerableHelpers.ToSet(_source, _comparer, cancellationToken));
}