Online PHP editor | output for aVrWS

<?php class ProductBase {} class Product extends ProductBase {} class ProductBlank extends ProductBase {} abstract class QuantityLineProductBase { /** * Contract: will always return some kind of ProductBase */ abstract public function getProduct(): ProductBase; } class QuantityLineProductProduct extends QuantityLineProductBase { private Product $product; /** * Constructor doesn't need to obey substitution principles */ public function __construct(Product $product) { $this->product = $product; } /** * Covariance of output; no violation */ public function getProduct(): Product { return $this->product; } } class QuantityLineProductBlank extends QuantityLineProductBase { private ProductBlank $product; /** * Constructor accepting a different type; no violation */ public function __construct(ProductBlank $product) { $this->product = $product; } /** * Covariance of output; no violation */ public function getProduct(): ProductBlank { return $this->product; } }