Returns the string version of the current Pair, which is "Pair"
public function __toString(): string;
Returns
string - The string "Pair".
Examples
The string version of a Pair is always "Pair":
$p = Pair {-1, 5};
echo $p->__toString()."\n";
$p2 = Pair {'foo', 'bar'};
echo $p2->__toString()."\n";