diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 81f1f2f..c7f2d07 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -15,7 +15,7 @@ jobs:
       fail-fast: false
       max-parallel: 3
       matrix:
-        php: ['7.4', '8.0', '8.1', '8.2']
+        php: ['8.1', '8.2']
     name: PHP ${{ matrix.php }} ${{ matrix.description }}
     steps:
       - name: Checkout
diff --git a/.github/workflows/coverage.yml b/.github/workflows/coverage.yml
index aadabde..c6ad76f 100644
--- a/.github/workflows/coverage.yml
+++ b/.github/workflows/coverage.yml
@@ -15,7 +15,7 @@ jobs:
       fail-fast: false
       max-parallel: 1
       matrix:
-        php: ['8.0']
+        php: ['8.1']
     name: PHP ${{ matrix.php }} ${{ matrix.description }}
     steps:
       - name: Checkout
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2afcd19..41c27ce 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,7 @@
 ## Changelog
+### v6.0.0
+- minimum required PHP version 8.1
+- added return types where possible
 ### v5.5.0
 - extractor configuration can now contain an array of extractors 
 ### v5.0.0
diff --git a/composer.json b/composer.json
index 7c9fc6b..6f03b62 100644
--- a/composer.json
+++ b/composer.json
@@ -20,10 +20,10 @@
         "bin/zf-dependency-injection-cache-warmup"
     ],
     "require": {
-        "php": "~7.4.0 || ~8.0.0 || ~8.1.0 || ~8.2.0",
+        "php": "~8.1.0 || ~8.2.0",
         "laminas/laminas-servicemanager": "^2.7 | ^3.0",
         "laminas/laminas-modulemanager": "^2.7",
-        "psr/simple-cache": "^1.0"
+        "psr/simple-cache": "^1.0 | ^2.0 | ^3.0"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/Annotation/AbstractInjectPluginManager.php b/src/Annotation/AbstractInjectPluginManager.php
index 3bc64c1..d334170 100644
--- a/src/Annotation/AbstractInjectPluginManager.php
+++ b/src/Annotation/AbstractInjectPluginManager.php
@@ -34,7 +34,7 @@ public function __construct(array $values)
         $this->name = $values['value'];
     }
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         $container = $this->determineContainer($container);
         $pluginManagerImplementation = $container->get(static::PLUGIN_MANAGER);
diff --git a/src/Annotation/Inject.php b/src/Annotation/Inject.php
index 0c33b84..126e8d3 100644
--- a/src/Annotation/Inject.php
+++ b/src/Annotation/Inject.php
@@ -14,12 +14,9 @@
  */
 final class Inject implements AnnotationInterface
 {
-    /**
-     * @var string
-     */
-    public $value;
+    public string $value;
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         return $container->get($this->value);
     }
diff --git a/src/Annotation/InjectConfig.php b/src/Annotation/InjectConfig.php
index 10c7c0c..a72baa9 100644
--- a/src/Annotation/InjectConfig.php
+++ b/src/Annotation/InjectConfig.php
@@ -29,7 +29,7 @@ public function __construct(array $values)
         $this->configPath = $values['value'];
     }
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         $container = $this->determineContainer($container);
 
diff --git a/src/Annotation/InjectConstant.php b/src/Annotation/InjectConstant.php
index 411c99f..94b65c3 100644
--- a/src/Annotation/InjectConstant.php
+++ b/src/Annotation/InjectConstant.php
@@ -14,12 +14,9 @@
  */
 final class InjectConstant implements AnnotationInterface
 {
-    /**
-     * @var string
-     */
-    public $value;
+    public string $value;
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         return constant($this->value);
     }
diff --git a/src/Annotation/InjectContainer.php b/src/Annotation/InjectContainer.php
index 8bc5efd..b62031d 100644
--- a/src/Annotation/InjectContainer.php
+++ b/src/Annotation/InjectContainer.php
@@ -14,7 +14,7 @@
  */
 final class InjectContainer implements AnnotationInterface
 {
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         return $container;
     }
diff --git a/src/Annotation/InjectDoctrineRepository.php b/src/Annotation/InjectDoctrineRepository.php
index 69b5ce9..9da0fde 100644
--- a/src/Annotation/InjectDoctrineRepository.php
+++ b/src/Annotation/InjectDoctrineRepository.php
@@ -4,6 +4,7 @@
 
 namespace Reinfi\DependencyInjection\Annotation;
 
+use Doctrine\ORM\EntityRepository;
 use Psr\Container\ContainerInterface;
 use Reinfi\DependencyInjection\Exception\AutoWiringNotPossibleException;
 
@@ -34,7 +35,7 @@ public function __construct(array $values)
         $this->entity = $values['value'];
     }
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): EntityRepository
     {
         $container = $this->determineContainer($container);
 
diff --git a/src/Annotation/InjectParent.php b/src/Annotation/InjectParent.php
index 7d5bec9..1af27ac 100644
--- a/src/Annotation/InjectParent.php
+++ b/src/Annotation/InjectParent.php
@@ -15,12 +15,9 @@
  */
 final class InjectParent implements AnnotationInterface
 {
-    /**
-     * @var string
-     */
-    public $value;
+    public string $value;
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         if ($container instanceof AbstractPluginManager) {
             $container = $container->getServiceLocator();
diff --git a/src/Attribute/AbstractInjectPluginManager.php b/src/Attribute/AbstractInjectPluginManager.php
index 07d7089..56122ce 100644
--- a/src/Attribute/AbstractInjectPluginManager.php
+++ b/src/Attribute/AbstractInjectPluginManager.php
@@ -25,7 +25,7 @@ public function __construct(string $name, ?array $options = null)
         $this->options = $options;
     }
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         $container = $this->determineContainer($container);
         $pluginManagerImplementation = $container->get(static::PLUGIN_MANAGER);
diff --git a/src/Attribute/Inject.php b/src/Attribute/Inject.php
index de2da4d..21ad16f 100644
--- a/src/Attribute/Inject.php
+++ b/src/Attribute/Inject.php
@@ -21,7 +21,7 @@ public function __construct(string $value)
         $this->value = $value;
     }
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         return $container->get($this->value);
     }
diff --git a/src/Attribute/InjectConfig.php b/src/Attribute/InjectConfig.php
index c7bd6d0..45bec33 100644
--- a/src/Attribute/InjectConfig.php
+++ b/src/Attribute/InjectConfig.php
@@ -25,7 +25,7 @@ public function __construct(string $configPath, bool $asArray = false)
         $this->asArray = $asArray;
     }
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         $container = $this->determineContainer($container);
 
diff --git a/src/Attribute/InjectConstant.php b/src/Attribute/InjectConstant.php
index d3f9267..ad7181a 100644
--- a/src/Attribute/InjectConstant.php
+++ b/src/Attribute/InjectConstant.php
@@ -21,7 +21,7 @@ public function __construct(string $value)
         $this->value = $value;
     }
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         return constant($this->value);
     }
diff --git a/src/Attribute/InjectContainer.php b/src/Attribute/InjectContainer.php
index 930dd9f..ac736a1 100644
--- a/src/Attribute/InjectContainer.php
+++ b/src/Attribute/InjectContainer.php
@@ -14,7 +14,7 @@
 #[Attribute(Attribute::TARGET_METHOD | Attribute::TARGET_PROPERTY | Attribute::IS_REPEATABLE)]
 final class InjectContainer implements InjectionInterface
 {
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): ContainerInterface
     {
         return $container;
     }
diff --git a/src/Attribute/InjectDoctrineRepository.php b/src/Attribute/InjectDoctrineRepository.php
index a89e4e5..0f1a51a 100644
--- a/src/Attribute/InjectDoctrineRepository.php
+++ b/src/Attribute/InjectDoctrineRepository.php
@@ -5,6 +5,7 @@
 namespace Reinfi\DependencyInjection\Attribute;
 
 use Attribute;
+use Doctrine\ORM\EntityRepository;
 use Psr\Container\ContainerInterface;
 use Reinfi\DependencyInjection\Exception\AutoWiringNotPossibleException;
 
@@ -27,7 +28,7 @@ public function __construct(string $entity, ?string $entityManager = null)
         }
     }
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): EntityRepository
     {
         $container = $this->determineContainer($container);
 
diff --git a/src/Attribute/InjectParent.php b/src/Attribute/InjectParent.php
index cf26d6e..4a8e580 100644
--- a/src/Attribute/InjectParent.php
+++ b/src/Attribute/InjectParent.php
@@ -22,7 +22,7 @@ public function __construct(string $value)
         $this->value = $value;
     }
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         if ($container instanceof AbstractPluginManager) {
             $container = $container->getServiceLocator();
diff --git a/src/Extension/PHPStan/ServiceManagerLoader.php b/src/Extension/PHPStan/ServiceManagerLoader.php
index 6765de3..160d3fc 100644
--- a/src/Extension/PHPStan/ServiceManagerLoader.php
+++ b/src/Extension/PHPStan/ServiceManagerLoader.php
@@ -10,10 +10,7 @@
 
 final class ServiceManagerLoader
 {
-    /**
-     * @var ServiceManager|null
-     */
-    private $serviceLocator = null;
+    private ?ServiceManager $serviceLocator = null;
 
     public function __construct(?string $serviceManagerLoader)
     {
diff --git a/src/Injection/AutoWiring.php b/src/Injection/AutoWiring.php
index 8ea3ec1..341d1ca 100644
--- a/src/Injection/AutoWiring.php
+++ b/src/Injection/AutoWiring.php
@@ -21,10 +21,9 @@ public function __construct(string $serviceName)
     }
 
     /**
-     * @return mixed
      * @throws AutoWiringNotPossibleException
      */
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         if ($container->has($this->serviceName)) {
             return $container->get($this->serviceName);
diff --git a/src/Injection/AutoWiringPluginManager.php b/src/Injection/AutoWiringPluginManager.php
index 7472f62..e21f78e 100644
--- a/src/Injection/AutoWiringPluginManager.php
+++ b/src/Injection/AutoWiringPluginManager.php
@@ -26,21 +26,20 @@ public function __construct(
     }
 
     /**
-     * @return mixed
      * @throws AutoWiringNotPossibleException
      */
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         if ($container instanceof AbstractPluginManager) {
             $container = $container->getServiceLocator();
         }
 
-        $pluginManagerImplemenation = $container->get($this->pluginManager);
+        $pluginManagerImplementation = $container->get($this->pluginManager);
         if (
-            $pluginManagerImplemenation instanceof ContainerInterface
-            && $pluginManagerImplemenation->has($this->serviceName)
+            $pluginManagerImplementation instanceof ContainerInterface
+            && $pluginManagerImplementation->has($this->serviceName)
         ) {
-            return $pluginManagerImplemenation->get($this->serviceName);
+            return $pluginManagerImplementation->get($this->serviceName);
         }
 
         throw new AutoWiringNotPossibleException($this->serviceName);
diff --git a/src/Injection/InjectionInterface.php b/src/Injection/InjectionInterface.php
index a6d9fbe..8e55256 100644
--- a/src/Injection/InjectionInterface.php
+++ b/src/Injection/InjectionInterface.php
@@ -13,8 +13,5 @@
  */
 interface InjectionInterface
 {
-    /**
-     * @return mixed
-     */
-    public function __invoke(ContainerInterface $container);
+    public function __invoke(ContainerInterface $container): mixed;
 }
diff --git a/src/Injection/Value.php b/src/Injection/Value.php
index 05cf3b4..690d1d5 100644
--- a/src/Injection/Value.php
+++ b/src/Injection/Value.php
@@ -11,20 +11,14 @@
  */
 class Value implements InjectionInterface
 {
-    /**
-     * @var mixed
-     */
-    private $value;
+    private mixed $value;
 
-    /**
-     * @param mixed $value
-     */
-    public function __construct($value)
+    public function __construct(mixed $value)
     {
         $this->value = $value;
     }
 
-    public function __invoke(ContainerInterface $container)
+    public function __invoke(ContainerInterface $container): mixed
     {
         return $this->value;
     }
diff --git a/src/Service/AutoWiring/Factory/ResolverServiceFactory.php b/src/Service/AutoWiring/Factory/ResolverServiceFactory.php
index 53d4d1c..0a6da82 100644
--- a/src/Service/AutoWiring/Factory/ResolverServiceFactory.php
+++ b/src/Service/AutoWiring/Factory/ResolverServiceFactory.php
@@ -37,7 +37,7 @@ public function __invoke(ContainerInterface $container): ResolverService
     }
 
     /**
-     * @return class-string[]
+     * @return class-string<ResolverInterface>[]
      */
     private function getResolverStack(array $config): array
     {
diff --git a/src/Service/AutoWiring/LazyResolverService.php b/src/Service/AutoWiring/LazyResolverService.php
index 984aee1..b02eed3 100644
--- a/src/Service/AutoWiring/LazyResolverService.php
+++ b/src/Service/AutoWiring/LazyResolverService.php
@@ -7,8 +7,6 @@
 use Psr\Container\ContainerInterface;
 
 /**
- * Class LazyResolverService
- *
  * @package Reinfi\DependencyInjection\Service\AutoWiring
  */
 class LazyResolverService implements ResolverServiceInterface
diff --git a/src/Service/Cache/Memory.php b/src/Service/Cache/Memory.php
index fd14422..dfda030 100644
--- a/src/Service/Cache/Memory.php
+++ b/src/Service/Cache/Memory.php
@@ -11,7 +11,7 @@ class Memory implements CacheInterface
 {
     private array $cachedItems = [];
 
-    public function get($key, $default = null)
+    public function get($key, $default = null): mixed
     {
         return $this->cachedItems[$key] ?? $default;
     }
diff --git a/src/Service/Extractor/Factory/ExtractorFactory.php b/src/Service/Extractor/Factory/ExtractorFactory.php
index bdfd1fc..668d14c 100644
--- a/src/Service/Extractor/Factory/ExtractorFactory.php
+++ b/src/Service/Extractor/Factory/ExtractorFactory.php
@@ -28,9 +28,7 @@ public function __invoke(ContainerInterface $container): ExtractorInterface
             $extractors[] = $container->get(AnnotationExtractor::class);
         }
 
-        if (version_compare(PHP_VERSION, '8.0.0') >= 0) {
-            $extractors[] = $container->get(AttributeExtractor::class);
-        }
+        $extractors[] = $container->get(AttributeExtractor::class);
 
         return new ExtractorChain($extractors);
     }
diff --git a/test/Unit/Service/Extractor/Factory/ExtractorFactoryTest.php b/test/Unit/Service/Extractor/Factory/ExtractorFactoryTest.php
index 5109b73..9edebd4 100644
--- a/test/Unit/Service/Extractor/Factory/ExtractorFactoryTest.php
+++ b/test/Unit/Service/Extractor/Factory/ExtractorFactoryTest.php
@@ -26,8 +26,6 @@ class ExtractorFactoryTest extends TestCase
 
     public function testItReturnsExtractorDefinedInConfig(): void
     {
-        $isPhp8OrAbove = version_compare(PHP_VERSION, '8.0.0') >= 0;
-
         $moduleConfig = new Config([
             'extractor' => YamlExtractor::class,
         ]);
@@ -48,7 +46,7 @@ public function testItReturnsExtractorDefinedInConfig(): void
             ->shouldBeCalled();
         $container->get(AttributeExtractor::class)
             ->willReturn($attributeExtractor->reveal())
-            ->shouldBeCalledTimes($isPhp8OrAbove ? 1 : 0);
+            ->shouldBeCalled();
 
         $factory = new ExtractorFactory();
 
@@ -64,19 +62,13 @@ public function testItReturnsExtractorDefinedInConfig(): void
 
         self::assertTrue(is_array($chain));
 
-        if ($isPhp8OrAbove) {
-            self::assertCount(3, $chain);
-        } else {
-            self::assertCount(2, $chain);
-        }
+        self::assertCount(3, $chain);
 
         self::assertContainsOnlyInstancesOf(ExtractorInterface::class, $chain);
     }
 
     public function testItReturnsArrayOfExtractorsDefinedInConfig(): void
     {
-        $isPhp8OrAbove = version_compare(PHP_VERSION, '8.0.0') >= 0;
-
         $moduleConfig = new Config([
             'extractor' => [
                 YamlExtractor::class,
@@ -99,7 +91,7 @@ public function testItReturnsArrayOfExtractorsDefinedInConfig(): void
             ->shouldBeCalled();
         $container->get(AttributeExtractor::class)
             ->willReturn($attributeExtractor->reveal())
-            ->shouldBeCalledTimes($isPhp8OrAbove ? 1 : 0);
+            ->shouldBeCalled();
 
         $factory = new ExtractorFactory();
 
@@ -115,19 +107,13 @@ public function testItReturnsArrayOfExtractorsDefinedInConfig(): void
 
         self::assertTrue(is_array($chain));
 
-        if ($isPhp8OrAbove) {
-            self::assertCount(3, $chain);
-        } else {
-            self::assertCount(2, $chain);
-        }
+        self::assertCount(3, $chain);
 
         self::assertContainsOnlyInstancesOf(ExtractorInterface::class, $chain);
     }
 
     public function testItReturnsAnnotationExtractorIfNoneDefined(): void
     {
-        $isPhp8OrAbove = version_compare(PHP_VERSION, '8.0.0') >= 0;
-
         $moduleConfig = new Config([]);
 
         $annotationExtractor = $this->prophesize(AnnotationExtractor::class);
@@ -142,7 +128,7 @@ public function testItReturnsAnnotationExtractorIfNoneDefined(): void
             ->shouldBeCalled();
         $container->get(AttributeExtractor::class)
             ->willReturn($attributeExtractor->reveal())
-            ->shouldBeCalledTimes($isPhp8OrAbove ? 1 : 0);
+            ->shouldBeCalled();
 
         $factory = new ExtractorFactory();
 
@@ -158,11 +144,7 @@ public function testItReturnsAnnotationExtractorIfNoneDefined(): void
 
         self::assertTrue(is_array($chain));
 
-        if ($isPhp8OrAbove) {
-            self::assertCount(2, $chain);
-        } else {
-            self::assertCount(1, $chain);
-        }
+        self::assertCount(2, $chain);
 
         self::assertInstanceOf(AnnotationExtractor::class, $chain[0]);