LSP

app/Solid/LSP/Bad/BeefItem.php

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+<?php
+
+namespace App\Solid\LSP\Bad;
+
+class BeefItem extends MenuItem
+{
+    public function __construct(int $price, string $name, string $description)
+    {
+        parent::__construct($price, $name, $description);
+    }
+}

app/Solid/LSP/Bad/BeverageItem.php

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+<?php
+
+namespace App\Solid\LSP\Bad;
+
+class BeverageItem extends MenuItem
+{
+    public function __construct(int $price, string $name, string $description)
+    {
+        parent::__construct($price, $name, $description);
+    }
+
+    public function getPriceWithDiscount(int $discountPercent){
+        return $this->price - ($this->price * $discountPercent/ 100);
+    }
+}

app/Solid/LSP/Bad/LiskovExample.php

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+<?php
+
+namespace App\Solid\LSP\Bad;
+
+class LiskovExample
+{
+    /**
+     * @throws \Exception
+     */
+    public function printItemPrice($item){
+        if($item instanceof BeverageItem){
+            echo "\nBeverage price:";
+            echo $item->getPriceWithDiscount(10);
+        }else if($item instanceof BeefItem){
+            echo "\nBeef price:";
+            echo $item->getPrice();
+        }else{
+            throw new \Exception("Item not found");
+        }
+    }
+
+    /**
+     * @throws \Exception
+     */
+    public function main(){
+        $beverageItem = new BeverageItem(200, "Orange","big");
+        $beefItem = new BeefItem(100, "Wagyu","small");
+
+        $this->printItemPrice($beverageItem);
+        $this->printItemPrice($beefItem);
+    }
+}

app/Solid/LSP/Bad/MenuItem.php

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+<?php
+
+namespace App\Solid\LSP\Bad;
+
+class MenuItem
+{
+
+    public int $price;
+    public string $name;
+    public string $description;
+
+
+    public function __construct(int $price, string $name, string $description)
+    {
+        $this->price = $price;
+        $this->name = $name;
+        $this->description = $description;
+    }
+
+    public function getPrice(){
+        return $this->price;
+    }
+}

app/Solid/LSP/Good/BeefItem.php

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+<?php
+
+namespace App\Solid\LSP\Good;
+
+class BeefItem extends MenuItem
+{
+    public function __construct(int $price, string $name, string $description)
+    {
+        parent::__construct($price, $name, $description);
+    }
+}

app/Solid/LSP/Good/BeverageItem.php

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+<?php
+
+namespace App\Solid\LSP\Good;
+
+class BeverageItem extends MenuItem
+{
+    public function __construct(int $price, string $name, string $description)
+    {
+        parent::__construct($price, $name, $description);
+    }
+
+    public function getPrice()
+    {
+        return $this->price - $this->getDiscount();
+    }
+
+    private function getDiscount(){
+        $discountPercent = 10;
+        return ($this->price * $discountPercent/ 100);
+    }
+}

app/Solid/LSP/Good/LiskovExample.php

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+<?php
+
+namespace App\Solid\LSP\Good;
+
+class LiskovExample
+{
+    /**
+     * @throws \Exception
+     */
+    public function printItemPrice($item){
+        if($item instanceof BeverageItem){
+            echo "\nBeverage price:";
+        }else if($item instanceof BeefItem){
+            echo "\nBeef price:";
+        }else{
+            throw new \Exception("Item not found");
+        }
+        echo $item->getPrice();
+    }
+
+    /**
+     * @throws \Exception
+     */
+    public function main(){
+        $beverageItem = new BeverageItem(200, "Orange","big");
+        $beefItem = new BeefItem(100, "Wagyu","small");
+
+        $this->printItemPrice($beverageItem);
+        $this->printItemPrice($beefItem);
+    }
+}

app/Solid/LSP/Good/MenuItem.php

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+<?php
+
+namespace App\Solid\LSP\Good;
+
+class MenuItem
+{
+
+    public int $price;
+    public string $name;
+    public string $description;
+
+
+    public function __construct(int $price, string $name, string $description)
+    {
+        $this->price = $price;
+        $this->name = $name;
+        $this->description = $description;
+    }
+
+    public function getPrice()
+    {
+        return $this->price - $this->getDiscount();
+    }
+
+    private function getDiscount(){
+        return 0;
+    }
+}