diff --git a/src/AutoMapperBundle.php b/src/AutoMapperBundle.php
index a0614b6..d468a3d 100644
--- a/src/AutoMapperBundle.php
+++ b/src/AutoMapperBundle.php
@@ -12,7 +12,7 @@
 
 class AutoMapperBundle extends Bundle
 {
-    public function build(ContainerBuilder $container)
+    public function build(ContainerBuilder $container): void
     {
         parent::build($container);
 
diff --git a/src/CacheWarmup/CacheWarmer.php b/src/CacheWarmup/CacheWarmer.php
index aa9bc6e..5c23bc2 100644
--- a/src/CacheWarmup/CacheWarmer.php
+++ b/src/CacheWarmup/CacheWarmer.php
@@ -12,28 +12,20 @@
  */
 final class CacheWarmer implements CacheWarmerInterface
 {
-    private $autoMapperRegistry;
-    /** @var iterable<CacheWarmerLoaderInterface> */
-    private $cacheWarmerLoaders;
-    private $autoMapperCacheDirectory;
-
     /** @param iterable<CacheWarmerLoaderInterface> $cacheWarmerLoaders */
     public function __construct(
-        AutoMapperRegistryInterface $autoMapperRegistry,
-        iterable $cacheWarmerLoaders,
-        string $autoMapperCacheDirectory
+        private readonly AutoMapperRegistryInterface $autoMapperRegistry,
+        private readonly iterable $cacheWarmerLoaders,
+        private readonly string $autoMapperCacheDirectory
     ) {
-        $this->autoMapperRegistry = $autoMapperRegistry;
-        $this->cacheWarmerLoaders = $cacheWarmerLoaders;
-        $this->autoMapperCacheDirectory = $autoMapperCacheDirectory;
     }
 
-    public function isOptional()
+    public function isOptional(): bool
     {
         return false;
     }
 
-    public function warmUp($cacheDir)
+    public function warmUp(string $cacheDir): array
     {
         foreach ($this->cacheWarmerLoaders as $cacheWarmerLoader) {
             foreach ($cacheWarmerLoader->loadCacheWarmupData() as $cacheWarmupData) {
diff --git a/src/DependencyInjection/Compiler/MapperConfigurationPass.php b/src/DependencyInjection/Compiler/MapperConfigurationPass.php
index 3fd8fa3..bcac2c2 100644
--- a/src/DependencyInjection/Compiler/MapperConfigurationPass.php
+++ b/src/DependencyInjection/Compiler/MapperConfigurationPass.php
@@ -11,7 +11,7 @@ class MapperConfigurationPass implements CompilerPassInterface
 {
     use PriorityTaggedServiceTrait;
 
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         $autoMapper = $container->getDefinition(AutoMapper::class);
 
diff --git a/src/DependencyInjection/Compiler/TransformerFactoryPass.php b/src/DependencyInjection/Compiler/TransformerFactoryPass.php
index 64794bc..a12e69a 100644
--- a/src/DependencyInjection/Compiler/TransformerFactoryPass.php
+++ b/src/DependencyInjection/Compiler/TransformerFactoryPass.php
@@ -11,7 +11,7 @@ class TransformerFactoryPass implements CompilerPassInterface
 {
     use PriorityTaggedServiceTrait;
 
-    public function process(ContainerBuilder $container)
+    public function process(ContainerBuilder $container): void
     {
         $definition = $container->getDefinition(ChainTransformerFactory::class);
 
diff --git a/src/DependencyInjection/Configuration.php b/src/DependencyInjection/Configuration.php
index f4cbb76..1a84f57 100644
--- a/src/DependencyInjection/Configuration.php
+++ b/src/DependencyInjection/Configuration.php
@@ -5,16 +5,14 @@
 use Symfony\Component\Config\Definition\Builder\TreeBuilder;
 use Symfony\Component\Config\Definition\ConfigurationInterface;
 
-class Configuration implements ConfigurationInterface
+readonly class Configuration implements ConfigurationInterface
 {
-    private $debug;
-
     /**
      * @param bool $debug Whether debugging is enabled or not
      */
-    public function __construct(bool $debug)
-    {
-        $this->debug = $debug;
+    public function __construct(
+        private bool $debug,
+    ) {
     }
 
     public function getConfigTreeBuilder(): TreeBuilder