src/Zicht/Itertools/lib/Traits/DifferenceTrait.php
public function difference($iterable, $strategy = null)
    {
        if ($this instanceof \Iterator) {
            return new DifferenceIterator(
                $this,
                conversions\mixed_to_iterator($iterable),
                conversions\mixed_to_value_getter($strategy)
            );
        }

        return null;
    }
public function difference($iterable, $strategy = null)
    {
        if ($this instanceof \Iterator) {
            return new DifferenceIterator(
                $this,
                conversions\mixed_to_iterator($iterable),
                conversions\mixed_to_value_getter($strategy)
            );
        }

        return null;
    }
Returns a DifferenceIterator containing elements in $this but not in $iterable

@param array|string|\Iterator $iterable
@param null|string|\Closure $strategy Optional
@return null|DifferenceIterator