public function join($separator)
    {
        return $this->reduce(
            function ($joined, $string) use ($separator) {
                return ('' === $joined ? '' : $joined . $separator) . $string;
            },
            ''
        );
    }
public function join($separator)
    {
        return $this->reduce(
            function ($joined, $string) use ($separator) {
                return ('' === $joined ? '' : $joined . $separator) . $string;
            },
            ''
        );
    }
public function join ( $ separator ) { return $ this -> reduce ( function ( $ joined , $ string ) use ( $ separator ) { return ( '' === $ joined ? '' : $ joined . $ separator ) . $ string ; } , '' ) ; }
Join all the strings in this map with the separator between them.

@param string $separator
@return string
@api
Join all the strings in this map with the separator between them .