php_demo/07面向对象/21协变和逆变/01协变.php

<?php
    /**
     * 还不能掌握什么是协变
     * 创建了一个animal的抽象类，留了speak叫这个动作给子类具体化
     * 创建一个dog类，继承了animal类，并且具体化了叫这个类，狗会吠，猫会喵
    */

    abstract class Animal{
        protected string $name;
        
        public function __construct(string $name){
            $this->name=$name;
        }
        
        abstract public function speak();
    }

    class Dog extends Animal{
        public function speak(){
            echo $this -> name." barks".PHP_EOL;
        }
    }

    class Cat extends Animal{
        public function speak(){
            echo $this->name." meows".PHP_EOL;
        }
    }

    $doggy=new Dog("旺财");
    $doggy->speak();


    
    interface AnimalShelter{
        public function adopt(string $name):Animal;
    }

    class CatShelter implements AnimalShelter{
        public function adopt(string $name):Cat{
            return new Cat($name);
        }
    }

    class DogShelter implements AnimalShelter{
        public function adopt(string $name):Dog{
            return new Dog($name);
        }
    }

    $kitty=(new CatShelter)->adopt("ricky");
    $kitty->speak();

    $doggy=(new DogShelter)->adopt("lucky");
    $doggy->speak();


    class Food{}

    class AnimalFood extends Food{}

    abstract class Animal{
        protected string $name;

        public function __construct(string $name){
            $this->name=$name;
        }

        public function eat(AnimalFood $food){
            echo $this->name."eats".get_class($food);
        }
    }

    class Dog extends Animal{
        public function eat(Food $food){
            echo $this->name."eats".get_class($food);
        }
    }

    $kitty=(new CatShelter)->adopt("ricky");
    $catFood=new AnimalFood();
    $kitty->eat($catFood).PHP_EOL;

    $doggy=(new DogShelter)->adopt("lucky");
    $banana=new Food();
    $doggy->eat($banana);

?>