diff --git a/src/EmailChecker/Adapter/ArrayAdapter.php b/src/EmailChecker/Adapter/ArrayAdapter.php
index adb341d..98adbe5 100644
--- a/src/EmailChecker/Adapter/ArrayAdapter.php
+++ b/src/EmailChecker/Adapter/ArrayAdapter.php
@@ -16,17 +16,23 @@
  *
  * @author Matthieu Moquet <matthieu@moquet.net>
  */
-final class ArrayAdapter implements AdapterInterface
+class ArrayAdapter implements AdapterInterface
 {
+    /**
+     * @var array<string, int>
+     */
+    private array $domainSet;
+
     /**
      * @param string[] $domains List of throwaway domains
      */
-    public function __construct(private array $domains)
+    public function __construct(array $domains)
     {
+        $this->domainSet = array_flip($domains);
     }
 
     public function isThrowawayDomain(string $domain): bool
     {
-        return in_array($domain, $this->domains, true);
+        return isset($this->domainSet[$domain]);
     }
 }
diff --git a/src/EmailChecker/Adapter/BuiltInAdapter.php b/src/EmailChecker/Adapter/BuiltInAdapter.php
index 16c10f4..ad8a9c8 100644
--- a/src/EmailChecker/Adapter/BuiltInAdapter.php
+++ b/src/EmailChecker/Adapter/BuiltInAdapter.php
@@ -23,27 +23,10 @@
  *
  * @author Matthieu Moquet <matthieu@moquet.net>
  */
-final class BuiltInAdapter implements AdapterInterface
+final class BuiltInAdapter extends ArrayAdapter
 {
-    /**
-     * @var string[]|null
-     */
-    protected array|null $domains = null;
-
-    public function isThrowawayDomain(string $domain): bool
+    public function __construct()
     {
-        return in_array($domain, $this->getDomains(), true);
-    }
-
-    /**
-     * @return string[]
-     */
-    private function getDomains(): array
-    {
-        if (null === $this->domains) {
-            $this->domains = (new ThrowawayDomains())->toArray();
-        }
-
-        return $this->domains;
+        parent::__construct((new ThrowawayDomains())->toArray());
     }
 }
diff --git a/src/EmailChecker/Adapter/FileAdapter.php b/src/EmailChecker/Adapter/FileAdapter.php
index 1313e6a..3b4ade0 100644
--- a/src/EmailChecker/Adapter/FileAdapter.php
+++ b/src/EmailChecker/Adapter/FileAdapter.php
@@ -18,13 +18,8 @@
  *
  * @author Matthieu Moquet <matthieu@moquet.net>
  */
-final class FileAdapter implements AdapterInterface
+final class FileAdapter extends ArrayAdapter
 {
-    /**
-     * @var string[]
-     */
-    protected array $domains;
-
     /**
      * @param string $filename Filename containing all domains
      */
@@ -35,11 +30,6 @@ public function __construct(string $filename)
             throw new \InvalidArgumentException(sprintf('File "%s" not found', $filename));
         }
 
-        $this->domains = Utilities::parseLines($content);
-    }
-
-    public function isThrowawayDomain(string $domain): bool
-    {
-        return in_array($domain, $this->domains, true);
+        parent::__construct(Utilities::parseLines($content));
     }
 }
diff --git a/src/EmailChecker/Adapter/GaufretteAdapter.php b/src/EmailChecker/Adapter/GaufretteAdapter.php
index d2715f6..df96145 100644
--- a/src/EmailChecker/Adapter/GaufretteAdapter.php
+++ b/src/EmailChecker/Adapter/GaufretteAdapter.php
@@ -19,20 +19,10 @@
  *
  * @author Matthieu Moquet <matthieu@moquet.net>
  */
-final class GaufretteAdapter implements AdapterInterface
+final class GaufretteAdapter extends ArrayAdapter
 {
-    /**
-     * @var string[]
-     */
-    private array $domains;
-
     public function __construct(File $file)
     {
-        $this->domains = Utilities::parseLines($file->getContent());
-    }
-
-    public function isThrowawayDomain(string $domain): bool
-    {
-        return in_array($domain, $this->domains, true);
+        parent::__construct(Utilities::parseLines($file->getContent()));
     }
 }