diff --git a/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php b/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
index f40a9806bf..b665aed4dc 100644
--- a/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/AbstractAdapter.php
@@ -107,7 +107,7 @@ abstract class AbstractAdapter implements AdapterInterface, CacheInterface, Logg
      *
      * @return AdapterInterface
      */
-    public static function createSystemCache($namespace, $defaultLifetime, $version, $directory, LoggerInterface $logger = null)
+    public static function createSystemCache(string $namespace, int $defaultLifetime, string $version, string $directory, LoggerInterface $logger = null)
     {
         $opcache = new PhpFilesAdapter($namespace, $defaultLifetime, $directory, true);
         if (null !== $logger) {
@@ -118,7 +118,7 @@ abstract class AbstractAdapter implements AdapterInterface, CacheInterface, Logg
             return $opcache;
         }
 
-        $apcu = new ApcuAdapter($namespace, (int) $defaultLifetime / 5, $version);
+        $apcu = new ApcuAdapter($namespace, $defaultLifetime / 5, $version);
         if ('cli' === \PHP_SAPI && !filter_var(ini_get('apc.enable_cli'), FILTER_VALIDATE_BOOLEAN)) {
             $apcu->setLogger(new NullLogger());
         } elseif (null !== $logger) {
@@ -128,11 +128,8 @@ abstract class AbstractAdapter implements AdapterInterface, CacheInterface, Logg
         return new ChainAdapter([$apcu, $opcache]);
     }
 
-    public static function createConnection($dsn, array $options = [])
+    public static function createConnection(string $dsn, array $options = [])
     {
-        if (!\is_string($dsn)) {
-            throw new InvalidArgumentException(sprintf('The %s() method expect argument #1 to be string, %s given.', __METHOD__, \gettype($dsn)));
-        }
         if (0 === strpos($dsn, 'redis:') || 0 === strpos($dsn, 'rediss:')) {
             return RedisAdapter::createConnection($dsn, $options);
         }
diff --git a/src/Symfony/Component/Cache/Adapter/ApcuAdapter.php b/src/Symfony/Component/Cache/Adapter/ApcuAdapter.php
index a9b599f05c..f7135aa148 100644
--- a/src/Symfony/Component/Cache/Adapter/ApcuAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/ApcuAdapter.php
@@ -80,7 +80,7 @@ class ApcuAdapter extends AbstractAdapter
     /**
      * {@inheritdoc}
      */
-    protected function doClear($namespace)
+    protected function doClear(string $namespace)
     {
         return isset($namespace[0]) && class_exists('APCuIterator', false) && ('cli' !== \PHP_SAPI || filter_var(ini_get('apc.enable_cli'), FILTER_VALIDATE_BOOLEAN))
             ? apcu_delete(new \APCuIterator(sprintf('/^%s/', preg_quote($namespace, '/')), APC_ITER_KEY))
@@ -102,7 +102,7 @@ class ApcuAdapter extends AbstractAdapter
     /**
      * {@inheritdoc}
      */
-    protected function doSave(array $values, $lifetime)
+    protected function doSave(array $values, int $lifetime)
     {
         try {
             if (false === $failures = apcu_store($values, null, $lifetime)) {
diff --git a/src/Symfony/Component/Cache/Adapter/DoctrineAdapter.php b/src/Symfony/Component/Cache/Adapter/DoctrineAdapter.php
index 80a8713e0e..7da759d4b7 100644
--- a/src/Symfony/Component/Cache/Adapter/DoctrineAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/DoctrineAdapter.php
@@ -73,7 +73,7 @@ class DoctrineAdapter extends AbstractAdapter
     /**
      * {@inheritdoc}
      */
-    protected function doClear($namespace)
+    protected function doClear(string $namespace)
     {
         $namespace = $this->provider->getNamespace();
 
@@ -98,7 +98,7 @@ class DoctrineAdapter extends AbstractAdapter
     /**
      * {@inheritdoc}
      */
-    protected function doSave(array $values, $lifetime)
+    protected function doSave(array $values, int $lifetime)
     {
         return $this->provider->saveMultiple($values, $lifetime);
     }
diff --git a/src/Symfony/Component/Cache/Adapter/MemcachedAdapter.php b/src/Symfony/Component/Cache/Adapter/MemcachedAdapter.php
index ce29d84bf2..a625215529 100644
--- a/src/Symfony/Component/Cache/Adapter/MemcachedAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/MemcachedAdapter.php
@@ -234,7 +234,7 @@ class MemcachedAdapter extends AbstractAdapter
     /**
      * {@inheritdoc}
      */
-    protected function doSave(array $values, $lifetime)
+    protected function doSave(array $values, int $lifetime)
     {
         if (!$values = $this->marshaller->marshall($values, $failed)) {
             return $failed;
@@ -300,7 +300,7 @@ class MemcachedAdapter extends AbstractAdapter
     /**
      * {@inheritdoc}
      */
-    protected function doClear($namespace)
+    protected function doClear(string $namespace)
     {
         return '' === $namespace && $this->getClient()->flush();
     }
diff --git a/src/Symfony/Component/Cache/Adapter/PdoAdapter.php b/src/Symfony/Component/Cache/Adapter/PdoAdapter.php
index 2bb4c4df6c..d1c0b75a42 100644
--- a/src/Symfony/Component/Cache/Adapter/PdoAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/PdoAdapter.php
@@ -251,7 +251,7 @@ class PdoAdapter extends AbstractAdapter implements PruneableInterface
     /**
      * {@inheritdoc}
      */
-    protected function doClear($namespace)
+    protected function doClear(string $namespace)
     {
         $conn = $this->getConnection();
 
@@ -292,7 +292,7 @@ class PdoAdapter extends AbstractAdapter implements PruneableInterface
     /**
      * {@inheritdoc}
      */
-    protected function doSave(array $values, $lifetime)
+    protected function doSave(array $values, int $lifetime)
     {
         if (!$values = $this->marshaller->marshall($values, $failed)) {
             return $failed;
diff --git a/src/Symfony/Component/Cache/Adapter/PhpFilesAdapter.php b/src/Symfony/Component/Cache/Adapter/PhpFilesAdapter.php
index ec84f5e2a1..57fb3b7311 100644
--- a/src/Symfony/Component/Cache/Adapter/PhpFilesAdapter.php
+++ b/src/Symfony/Component/Cache/Adapter/PhpFilesAdapter.php
@@ -199,7 +199,7 @@ class PhpFilesAdapter extends AbstractAdapter implements PruneableInterface
     /**
      * {@inheritdoc}
      */
-    protected function doSave(array $values, $lifetime)
+    protected function doSave(array $values, int $lifetime)
     {
         $ok = true;
         $expiry = $lifetime ? time() + $lifetime : 'PHP_INT_MAX';
@@ -256,7 +256,7 @@ class PhpFilesAdapter extends AbstractAdapter implements PruneableInterface
     /**
      * {@inheritdoc}
      */
-    protected function doClear($namespace)
+    protected function doClear(string $namespace)
     {
         $this->values = [];
 
diff --git a/src/Symfony/Component/Cache/Adapter/Psr16Adapter.php b/src/Symfony/Component/Cache/Adapter/Psr16Adapter.php
index bb38871019..333c4af174 100644
--- a/src/Symfony/Component/Cache/Adapter/Psr16Adapter.php
+++ b/src/Symfony/Component/Cache/Adapter/Psr16Adapter.php
@@ -63,7 +63,7 @@ class Psr16Adapter extends AbstractAdapter implements PruneableInterface, Resett
     /**
      * {@inheritdoc}
      */
-    protected function doClear($namespace)
+    protected function doClear(string $namespace)
     {
         return $this->pool->clear();
     }
@@ -79,7 +79,7 @@ class Psr16Adapter extends AbstractAdapter implements PruneableInterface, Resett
     /**
      * {@inheritdoc}
      */
-    protected function doSave(array $values, $lifetime)
+    protected function doSave(array $values, int $lifetime)
     {
         return $this->pool->setMultiple($values, 0 === $lifetime ? null : $lifetime);
     }
diff --git a/src/Symfony/Component/Cache/DataCollector/CacheDataCollector.php b/src/Symfony/Component/Cache/DataCollector/CacheDataCollector.php
index 0f708f0859..0467dbeb96 100644
--- a/src/Symfony/Component/Cache/DataCollector/CacheDataCollector.php
+++ b/src/Symfony/Component/Cache/DataCollector/CacheDataCollector.php
@@ -33,7 +33,7 @@ class CacheDataCollector extends DataCollector implements LateDataCollectorInter
      * @param string           $name
      * @param TraceableAdapter $instance
      */
-    public function addInstance($name, TraceableAdapter $instance)
+    public function addInstance(string $name, TraceableAdapter $instance)
     {
         $this->instances[$name] = $instance;
     }
diff --git a/src/Symfony/Component/Cache/DependencyInjection/CachePoolPass.php b/src/Symfony/Component/Cache/DependencyInjection/CachePoolPass.php
index 5d7a2369c2..68e9587648 100644
--- a/src/Symfony/Component/Cache/DependencyInjection/CachePoolPass.php
+++ b/src/Symfony/Component/Cache/DependencyInjection/CachePoolPass.php
@@ -148,7 +148,7 @@ class CachePoolPass implements CompilerPassInterface
         }
     }
 
-    private function getNamespace($seed, $id)
+    private function getNamespace(string $seed, string $id)
     {
         return substr(str_replace('/', '-', base64_encode(hash('sha256', $id.$seed, true))), 0, 10);
     }
diff --git a/src/Symfony/Component/Cache/Marshaller/DefaultMarshaller.php b/src/Symfony/Component/Cache/Marshaller/DefaultMarshaller.php
index 9c1ef46015..328971953f 100644
--- a/src/Symfony/Component/Cache/Marshaller/DefaultMarshaller.php
+++ b/src/Symfony/Component/Cache/Marshaller/DefaultMarshaller.php
@@ -92,7 +92,7 @@ class DefaultMarshaller implements MarshallerInterface
     /**
      * @internal
      */
-    public static function handleUnserializeCallback($class)
+    public static function handleUnserializeCallback(string $class)
     {
         throw new \DomainException('Class not found: '.$class);
     }
diff --git a/src/Symfony/Component/Cache/Traits/AbstractAdapterTrait.php b/src/Symfony/Component/Cache/Traits/AbstractAdapterTrait.php
index c11f53257a..1291acfae3 100644
--- a/src/Symfony/Component/Cache/Traits/AbstractAdapterTrait.php
+++ b/src/Symfony/Component/Cache/Traits/AbstractAdapterTrait.php
@@ -61,7 +61,7 @@ trait AbstractAdapterTrait
      *
      * @return bool True if item exists in the cache, false otherwise
      */
-    abstract protected function doHave($id);
+    abstract protected function doHave(string $id);
 
     /**
      * Deletes all items in the pool.
@@ -70,7 +70,7 @@ trait AbstractAdapterTrait
      *
      * @return bool True if the pool was successfully cleared, false otherwise
      */
-    abstract protected function doClear($namespace);
+    abstract protected function doClear(string $namespace);
 
     /**
      * Removes multiple items from the pool.
@@ -89,7 +89,7 @@ trait AbstractAdapterTrait
      *
      * @return array|bool The identifiers that failed to be cached or a boolean stating if caching succeeded or not
      */
-    abstract protected function doSave(array $values, $lifetime);
+    abstract protected function doSave(array $values, int $lifetime);
 
     /**
      * {@inheritdoc}
diff --git a/src/Symfony/Component/Cache/Traits/FilesystemCommonTrait.php b/src/Symfony/Component/Cache/Traits/FilesystemCommonTrait.php
index 37e1fd1f06..2f953a89c4 100644
--- a/src/Symfony/Component/Cache/Traits/FilesystemCommonTrait.php
+++ b/src/Symfony/Component/Cache/Traits/FilesystemCommonTrait.php
@@ -51,7 +51,7 @@ trait FilesystemCommonTrait
     /**
      * {@inheritdoc}
      */
-    protected function doClear($namespace)
+    protected function doClear(string $namespace)
     {
         $ok = true;
 
diff --git a/src/Symfony/Component/Cache/Traits/FilesystemTrait.php b/src/Symfony/Component/Cache/Traits/FilesystemTrait.php
index 9c444f9b04..90c2f2e442 100644
--- a/src/Symfony/Component/Cache/Traits/FilesystemTrait.php
+++ b/src/Symfony/Component/Cache/Traits/FilesystemTrait.php
@@ -91,7 +91,7 @@ trait FilesystemTrait
     /**
      * {@inheritdoc}
      */
-    protected function doSave(array $values, $lifetime)
+    protected function doSave(array $values, int $lifetime)
     {
         $expiresAt = $lifetime ? (time() + $lifetime) : 0;
         $values = $this->marshaller->marshall($values, $failed);
diff --git a/src/Symfony/Component/Cache/Traits/RedisTrait.php b/src/Symfony/Component/Cache/Traits/RedisTrait.php
index 6f6d94bbe8..46f3ddd736 100644
--- a/src/Symfony/Component/Cache/Traits/RedisTrait.php
+++ b/src/Symfony/Component/Cache/Traits/RedisTrait.php
@@ -332,7 +332,7 @@ trait RedisTrait
     /**
      * {@inheritdoc}
      */
-    protected function doClear($namespace)
+    protected function doClear(string $namespace)
     {
         $cleared = true;
         if ($this->redis instanceof \Predis\Client) {
@@ -399,7 +399,7 @@ trait RedisTrait
     /**
      * {@inheritdoc}
      */
-    protected function doSave(array $values, $lifetime)
+    protected function doSave(array $values, int $lifetime)
     {
         if (!$values = $this->marshaller->marshall($values, $failed)) {
             return $failed;