Add isSupported() method

lib/EioDriver.php

@@ -11,6 +11,14 @@ class EioDriver implements Driver
     /** @var \Amp\File\Internal\EioPoll */
     private $poll;
 
+    /**
+     * @return bool Determines if this driver can be used based on the environment.
+     */
+    public static function isSupported(): bool
+    {
+        return \extension_loaded('eio');
+    }
+
     public function __construct()
     {
         $this->poll = new Internal\EioPoll;

lib/UvDriver.php

@@ -20,6 +20,16 @@ class UvDriver implements Driver
     /** @var UvPoll */
     private $poll;
 
+    /**
+     * @param \Amp\Loop\Driver The currently active loop driver.
+     *
+     * @return bool Determines if this driver can be used based on the environment.
+     */
+    public static function isSupported(Loop\Driver $driver): bool
+    {
+        return $driver instanceof Loop\UvDriver;
+    }
+
     /**
      * @param \Amp\Loop\UvDriver $driver
      */

lib/functions.php

@@ -41,11 +41,11 @@ function driver(): Driver
 {
     $driver = Loop::get();
 
-    if ($driver instanceof Loop\UvDriver) {
+    if (UvDriver::isSupported($driver)) {
         return new UvDriver($driver);
     }
 
-    if (\extension_loaded("eio")) {
+    if (EioDriver::isSupported()) {
         return new EioDriver;
     }