public function distinctUntilChanged(callable $keySelector = null, callable $comparer = null)
    {
        return $this->lift(function () use ($keySelector, $comparer) {
            return new DistinctUntilChangedOperator($keySelector, $comparer);
        });
    }
public function distinctUntilChanged(callable $keySelector = null, callable $comparer = null)
    {
        return $this->lift(function () use ($keySelector, $comparer) {
            return new DistinctUntilChangedOperator($keySelector, $comparer);
        });
    }
public function distinctUntilChanged ( callable $ keySelector = null , callable $ comparer = null ) { return $ this -> lift ( function ( ) use ( $ keySelector , $ comparer ) { return new DistinctUntilChangedOperator ( $ keySelector , $ comparer ) ; } ) ; }
Returns an observable sequence that contains only distinct contiguous elements according to the keySelector
and the comparer.

@param callable $keySelector
@param callable $comparer
@return \Rx\Observable\AnonymousObservable
Returns an observable sequence that contains only distinct contiguous elements according to the keySelector and the comparer .