Init

.gitignore

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+.idea
+.DS_Store

1-single-responsibility-principle.php

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+<?php
+
+// Single Responsibility Principle Violation
+class Report
+{
+    public function getTitle()
+    {
+        return 'Report Title';
+    }
+
+    public function getDate()
+    {
+        return '2016-04-21';
+    }
+
+    public function getContents()
+    {
+        return [
+            'title' => $this->getTitle(),
+            'date' => $this->getDate(),
+        ];
+    }
+
+    public function formatJson()
+    {
+        return json_encode($this->getContents());
+    }
+}
+
+// Refactored
+class Report
+{
+    public function getTitle()
+    {
+        return 'Report Title';
+    }
+
+    public function getDate()
+    {
+        return '2016-04-21';
+    }
+
+    public function getContents()
+    {
+        return [
+            'title' => $this->getTitle(),
+            'date' => $this->getDate(),
+        ];
+    }
+}
+
+interface ReportFormattable
+{
+    public function format(Report $report);
+}
+
+class JsonReportFormatter implements ReportFormattable
+{
+    public function format(Report $report)
+    {
+        return json_encode($report->getContents());
+    }
+}

2-open-closed-principle.php

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+<?php
+
+// Open Closed Principle Violation
+class Programmer
+{
+    public function code()
+    {
+        return 'coding';
+    }
+}
+
+class Tester
+{
+    public function test()
+    {
+        return 'testing';
+    }
+}
+
+class ProjectManagement
+{
+    public function process($member)
+    {
+        if ($member instanceof Programmer) {
+            $member->code();
+        } elseif ($member instanceof Tester) {
+            $member->test();
+        };
+
+        throw new Exception('Invalid input member');
+    }
+}
+
+// Refactored
+interface Workable
+{
+    public function work();
+}
+
+class Programmer implements Workable
+{
+    public function work()
+    {
+        return 'coding';
+    }
+}
+
+class Tester implements Workable
+{
+    public function work()
+    {
+        return 'testing';
+    }
+}
+
+class ProjectManagement
+{
+    public function process(Workable $member)
+    {
+        return $member->work();
+    }
+}

3-liskov-substitution-principle.php

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+<?php
+
+// Liskov Substitution Principle Violation
+// The Rectangle - Square problem
+class Rectangle
+{
+    protected $width;
+    protected $height;
+
+    public function setHeight($height)
+    {
+        $this->height = $height;
+    }
+
+    public function getHeight()
+    {
+        return $this->height;
+    }
+
+    public function setWidth($width)
+    {
+        $this->width = $width;
+    }
+
+    public function getWidth()
+    {
+        return $this->width;
+    }
+
+    public function area()
+    {
+         return $this->height * $this->width;
+    }
+}
+
+class Square extends Rectangle
+{
+    public function setHeight($value)
+    {
+        $this->width = $value;
+        $this->height = $value;
+    }
+
+    public function setWidth($value)
+    {
+        $this->width = $value;
+        $this->height = $value;
+    }
+}
+
+class RectangleTest
+{
+    private $rectangle;
+
+    public function __construct(Rectangle $rectangle)
+    {
+        $this->rectangle = $rectangle;
+    }
+
+    public function testArea()
+    {
+        $this->rectangle->setHeight(2);
+        $this->rectangle->setWidth(3);
+        // Expect rectangle's area to be 6
+    }
+}

4-interface-segregation-principle.php

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+<?php
+
+// Interface Segregation Principle Violation
+interface Workable
+{
+    public function code();
+    public function test();
+}
+
+class Programmer implements Workable
+{
+    public function canCode()
+    {
+        return true;
+    }
+
+    public function code()
+    {
+        return 'coding';
+    }
+
+    public function test()
+    {
+        return 'testing in localhost';
+    }
+}
+
+class Tester implements Workable
+{
+    public function canCode()
+    {
+        return false;
+    }
+
+    public function code()
+    {
+         throw new Exception('Opps! I can not code');
+    }
+
+    public function test()
+    {
+        return 'testing in test server';
+    }
+}
+
+class ProjectManagement
+{
+    public function processCode(Workable $member)
+    {
+        if ($member->canCode()) {
+            $member->code();
+        }
+    }
+}
+
+// Refactored
+interface Codeable
+{
+    public function code();
+}
+
+interface Testable
+{
+    public function test();
+}
+
+class Programmer implements Codeable, Testable
+{
+    public function code()
+    {
+        return 'coding';
+    }
+
+    public function test()
+    {
+        return 'testing in localhost';
+    }
+}
+
+class Tester implements Workable
+{
+    public function test()
+    {
+        return 'testing in test server';
+    }
+}
+
+class ProjectManagement
+{
+    public function processCode(Codeable $member)
+    {
+        $member->code();
+    }
+}

5-dependency-inversion-principle.php

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+<?php
+// Dependency Inversion Principle Violation
+class Mailer
+{
+
+}
+
+class SendWelcomeMessage
+{
+    private $mailer;
+
+    public function __construct(Mailer $mailer)
+    {
+        $this->mailer = $mailer;
+    }
+}
+
+// Refactored
+interface Mailer
+{
+    public function send();
+}
+
+class SmtpMailer implements Mailer
+{
+    public function send()
+    {
+
+    }
+}
+
+class SendGridMailer implements Mailer
+{
+    public function send()
+    {
+
+    }
+}
+
+class SendWelcomeMessage
+{
+    private $mailer;
+
+    public function __construct(Mailer $mailer)
+    {
+        $this->mailer = $mailer;
+    }
+}

readme.md

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+## SOLID Principles Examples in PHP
+
+### Single Responsibility Principle
+A class should have one, and only one, reason to change. [Example](./1-single-responsibility-principle.php)
+
+### Open Closed Principle
+A class should be open for extension, but closed for modification. [Example](./2-open-closed-principle.php)
+
+### Liskov Substitution Principle
+Derived classes must be substitutable for their base classes. [Example](./3-liskov-substitution-principle.php)
+
+### Interface Segregation Principle
+Many client-specific interfaces are better than one general-purpose interface. [Example](./4-interface-segregation-principle.php)
+
+### Dependency Inversion Principle
+Depend upon abstractions. Do not depend upon concretions. [Example](./5-dependency-inversion-principle.php)
+
+#### For more information about *Object Oriented Design Principles*, you can refer [this slide](https://viblo.asia/thangtd90/posts/pVYRPJPmG4ng)