feat: support for optional constructor parameters

Author: fadrian06

src/Container.php

@@ -90,13 +90,12 @@ private function resolve(string $id): object
     }
 
     $dependencies = array_map(
-      function (ReflectionParameter $reflectionParameter) use ($id): ?object {
+      function (ReflectionParameter $reflectionParameter) use ($id) {
         $name = $reflectionParameter->getName();
         $type = $reflectionParameter->getType();
-        $isOptional = $reflectionParameter->isOptional();
 
-        if ($isOptional) {
-          return null;
+        if ($reflectionParameter->isOptional()) {
+          return $reflectionParameter->getDefaultValue();
         }
 
         if (!$type) {

tests/ContainerTest.php

@@ -139,6 +139,16 @@ public function test_it_throws_an_exception_when_the_class_has_a_union_type_hint
     $container->get(ExampleClassWithUnionTypeHint::class);
   }
 
+  public function test_it_resolves_optional_non_builtin_classes_constructor_parameters(): void
+  {
+    $container = new Container;
+
+    self::assertInstanceOf(
+      ExampleClassWithAnOptionalConstructorParameter::class,
+      $container->get(ExampleClassWithAnOptionalConstructorParameter::class)
+    );
+  }
+
   /** @return array{0: class-string}[] */
   public static function nonInstantiableClassStringsDataProvider(): array
   {
@@ -180,8 +190,7 @@ public function __construct($parameter)
 
 final class ExampleClassWithBuiltinConstructorParameter
 {
-  /** @var int */
-  public $parameter;
+  public int $parameter;
 
   public function __construct(int $parameter)
   {
@@ -191,15 +200,24 @@ public function __construct(int $parameter)
 
 final class ExampleClassWithAnNonBuiltinConstructorParameter
 {
-  /** @var DateTimeImmutable */
-  public $dateTime;
+  public DateTimeImmutable $dateTime;
 
   public function __construct(DateTimeImmutable $dateTimeImmutable)
   {
     $this->dateTime = $dateTimeImmutable;
   }
 }
 
+final class ExampleClassWithAnOptionalConstructorParameter
+{
+  public string $parameter;
+
+  public function __construct(string $parameter = 'default')
+  {
+    $this->parameter = $parameter;
+  }
+}
+
 if (PHP_VERSION >= '8.0') {
   require_once __DIR__ . '/ExampleClassWithUnionTypeHint.php';
 }