The unfinished parent

1<?php2interface Shape { public function area(): float; }3abstract class Base implements Shape {4    public function describe(): string {5        return static::class . ' area ' . $this->area();6    }7}8class Square extends Base {9    public function __construct(private float $side) {}10    public function area(): float { return $this->side * $this->side; }11}12try {13    new Base();14} catch (Error $e) {15    echo $e->getMessage(), "\n";16}17$s = new Square(3);18echo $s->describe(), "\n";19echo $s instanceof Shape ? 'is a Shape' : 'no', "\n";