add: DI singleton with tests

README.md

@@ -3,6 +3,7 @@
 Alpha version (in development).
 
 Features:
+- DI Container (thanks to Brent Rose)
 - Request
 - Response with content type changing (Json by default)
 - ResponseEmitter

core/DI/Contracts/Container.php

@@ -1,12 +1,17 @@
 <?php
 
+/**
+ * @author Brent Rose (https://github.com/brendt)
+ */
+
 declare(strict_types=1);
 
 namespace Twent\Framework\DI\Contracts;
 
 interface Container
 {
     public function register(string $className, callable $definition): self;
+    public function singleton(string $className, callable $definition): self;
 
     /**
      * @template TClassName

core/DI/GenericContainer.php

@@ -1,5 +1,9 @@
 <?php
 
+/**
+ * @author Brent Rose (https://github.com/brendt)
+ */
+
 declare(strict_types=1);
 
 namespace Twent\Framework\DI;
@@ -12,6 +16,7 @@
 final class GenericContainer implements Container
 {
     private array $definitions = [];
+    private array $singletons = [];
 
     public function register(string $className, callable $definition): Container
     {
@@ -20,11 +25,26 @@ public function register(string $className, callable $definition): Container
         return $this;
     }
 
+    public function singleton(string $className, callable $definition): Container
+    {
+        $this->definitions[$className] = function () use ($className, $definition) {
+            $instance = $definition($this);
+            $this->singletons[$className] = $instance;
+            return $instance;
+        };
+
+        return $this;
+    }
+
     /**
      * @inheritDoc
      */
     public function get(string $className): object
     {
+        if ($instance = ($this->singletons[$className] ?? null)) {
+            return $instance;
+        }
+
         $definition = $this->definitions[$className] ?? $this->autowire(...);
 
         return $definition($className);

tests/Feature/DI/GenericContainerTest.php

@@ -28,4 +28,18 @@ public function testContainerAutowire(): void
 
         $this->assertInstanceOf(Bar::class, $bar);
     }
+
+    public function testSingleton(): void
+    {
+        $container = new GenericContainer();
+
+        $container->singleton(SingletonExample::class, fn() => new SingletonExample());
+        $instance = $container->get(SingletonExample::class);
+
+        $this->assertInstanceOf(SingletonExample::class, $instance);
+        $this->assertEquals(1, $instance::$count);
+
+        $this->assertInstanceOf(SingletonExample::class, $instance);
+        $this->assertEquals(1, $instance::$count);
+    }
 }

tests/Feature/DI/SingletonExample.php

@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Twent\Framework\Feature\DI;
+
+final class SingletonExample
+{
+    public static int $count = 0;
+
+    public function __construct()
+    {
+        self::$count += 1;
+    }
+}