public function keyOf($value)
    {
        foreach ($this->items as $key => $iValue) {
            if ($value === $iValue) {
                return $key;
            }
        }

        return null;
    }
public function keyOf($value)
    {
        foreach ($this->items as $key => $iValue) {
            if ($value === $iValue) {
                return $key;
            }
        }

        return null;
    }
public function keyOf ( $ value ) { foreach ( $ this -> items as $ key => $ iValue ) { if ( $ value === $ iValue ) { return $ key ; } } return null ; }
Get the key of a value if exists.


@return mixed|null
Get the key of a value if exists .