Make watcher ID first parameter

trowski · trowski · commit ffde57f0d146 · 2016-05-19T10:30:38.000-05:00
diff --git a/src/Loop.php b/src/Loop.php
@@ -59,7 +59,7 @@ public static function stop()
     /**
      * Defer the execution of a callback.
      *
-     * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to defer.
+     * @param callable(string $watcherId, mixed $data) $callback The callback to defer.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
      * @return string An identifier that can be used to cancel, enable or disable the watcher.
@@ -72,7 +72,7 @@ public static function defer(callable $callback, $data = null)
     /**
      * Delay the execution of a callback. The time delay is approximate and accuracy is not guaranteed.
      *
-     * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to delay.
+     * @param callable(string $watcherId, mixed $data) $callback The callback to delay.
      * @param int $time The amount of time, in milliseconds, to delay the execution for.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
@@ -86,7 +86,7 @@ public static function delay(callable $callback, $time, $data = null)
     /**
      * Repeatedly execute a callback. The interval between executions is approximate and accuracy is not guaranteed.
      *
-     * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to repeat.
+     * @param callable(string $watcherId, mixed $data) $callback The callback to repeat.
      * @param int $interval The time interval, in milliseconds, to wait between executions.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
@@ -101,7 +101,7 @@ public static function repeat(callable $callback, $interval, $data = null)
      * Execute a callback when a stream resource becomes readable.
      *
      * @param resource $stream The stream to monitor.
-     * @param callable(resource $stream, mixed $data, string $watcherIdentifier) $callback The callback to execute.
+     * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
      * @return string An identifier that can be used to cancel, enable or disable the watcher.
@@ -115,7 +115,7 @@ public static function onReadable($stream, callable $callback, $data = null)
      * Execute a callback when a stream resource becomes writable.
      *
      * @param resource $stream The stream to monitor.
-     * @param callable(resource $stream, mixed $data, string $watcherIdentifier) $callback The callback to execute.
+     * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
      * @return string An identifier that can be used to cancel, enable or disable the watcher.
@@ -129,7 +129,7 @@ public static function onWritable($stream, callable $callback, $data = null)
      * Execute a callback when a signal is received.
      *
      * @param int $signo The signal number to monitor.
-     * @param callable(int $signo, mixed $data, string $watcherIdentifier) $callback The callback to execute.
+     * @param callable(string $watcherId, int $signo, mixed $data) $callback The callback to execute.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
      * @return string An identifier that can be used to cancel, enable or disable the watcher.
@@ -154,37 +154,37 @@ public static function onError(callable $callback)
     /**
      * Enable a watcher.
      *
-     * @param string $watcherIdentifier The watcher identifier.
+     * @param string $watcherId The watcher identifier.
      *
      * @return void
      */
-    public static function enable($watcherIdentifier)
+    public static function enable($watcherId)
     {
-        self::get()->enable($watcherIdentifier);
+        self::get()->enable($watcherId);
     }
 
     /**
      * Disable a watcher.
      *
-     * @param string $watcherIdentifier The watcher identifier.
+     * @param string $watcherId The watcher identifier.
      *
      * @return void
      */
-    public static function disable($watcherIdentifier)
+    public static function disable($watcherId)
     {
-        self::get()->disable($watcherIdentifier);
+        self::get()->disable($watcherId);
     }
 
     /**
      * Cancel a watcher.
      *
-     * @param string $watcherIdentifier The watcher identifier.
+     * @param string $watcherId The watcher identifier.
      *
      * @return void
      */
-    public static function cancel($watcherIdentifier)
+    public static function cancel($watcherId)
     {
-        self::get()->cancel($watcherIdentifier);
+        self::get()->cancel($watcherId);
     }
 
     /**
@@ -193,13 +193,13 @@ public static function cancel($watcherIdentifier)
      * This will keep the event loop alive whilst the event is still being monitored. Watchers have this state by
      * default.
      *
-     * @param string $watcherIdentifier The watcher identifier.
+     * @param string $watcherId The watcher identifier.
      *
      * @return void
      */
-    public static function reference($watcherIdentifier)
+    public static function reference($watcherId)
     {
-        self::get()->reference($watcherIdentifier);
+        self::get()->reference($watcherId);
     }
 
     /**
@@ -208,13 +208,13 @@ public static function reference($watcherIdentifier)
      * The event loop should exit the run method when only unreferenced watchers are still being monitored. Events are
      * all referenced by default.
      *
-     * @param string $watcherIdentifier The watcher identifier.
+     * @param string $watcherId The watcher identifier.
      *
      * @return void
      */
-    public static function unreference($watcherIdentifier)
+    public static function unreference($watcherId)
     {
-        self::get()->unreference($watcherIdentifier);
+        self::get()->unreference($watcherId);
     }
 
     /**
diff --git a/src/LoopDriver.php b/src/LoopDriver.php
@@ -23,7 +23,7 @@ public function stop();
     /**
      * Defer the execution of a callback.
      *
-     * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to defer.
+     * @param callable(string $watcherId, mixed $data) $callback The callback to defer.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
      * @return string An identifier that can be used to cancel, enable or disable the watcher.
@@ -33,7 +33,7 @@ public function defer(callable $callback, $data = null);
     /**
      * Delay the execution of a callback. The time delay is approximate and accuracy is not guaranteed.
      *
-     * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to delay.
+     * @param callable(string $watcherId, mixed $data) $callback The callback to delay.
      * @param int $delay The amount of time, in milliseconds, to delay the execution for.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
@@ -44,7 +44,7 @@ public function delay(callable $callback, $delay, $data = null);
     /**
      * Repeatedly execute a callback. The interval between executions is approximate and accuracy is not guaranteed.
      *
-     * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to repeat.
+     * @param callable(string $watcherId, mixed $data) $callback The callback to repeat.
      * @param int $interval The time interval, in milliseconds, to wait between executions.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
@@ -56,7 +56,7 @@ public function repeat(callable $callback, $interval, $data = null);
      * Execute a callback when a stream resource becomes readable.
      *
      * @param resource $stream The stream to monitor.
-     * @param callable(resource $stream, mixed $data, string $watcherIdentifier) $callback The callback to execute.
+     * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
      * @return string An identifier that can be used to cancel, enable or disable the watcher.
@@ -67,7 +67,7 @@ public function onReadable($stream, callable $callback, $data = null);
      * Execute a callback when a stream resource becomes writable.
      *
      * @param resource $stream The stream to monitor.
-     * @param callable(resource $stream, mixed $data, string $watcherIdentifier) $callback The callback to execute.
+     * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
      * @return string An identifier that can be used to cancel, enable or disable the watcher.
@@ -78,7 +78,7 @@ public function onWritable($stream, callable $callback, $data = null);
      * Execute a callback when a signal is received.
      *
      * @param int $signo The signal number to monitor.
-     * @param callable(int $signo, mixed $data, string $watcherIdentifier) $callback The callback to execute.
+     * @param callable(string $watcherId, int $signo, mixed $data) $callback The callback to execute.
      * @param mixed $data Arbitrary data given to the callback function as the $data parameter.
      *
      * @return string An identifier that can be used to cancel, enable or disable the watcher.
@@ -97,52 +97,52 @@ public function onError(callable $callback);
     /**
      * Enable a watcher.
      *
-     * @param string $watcherIdentifier The watcher identifier.
+     * @param string $watcherId The watcher identifier.
      *
      * @return void
      */
-    public function enable($watcherIdentifier);
+    public function enable($watcherId);
 
     /**
      * Disable a watcher.
      *
-     * @param string $watcherIdentifier The watcher identifier.
+     * @param string $watcherId The watcher identifier.
      *
      * @return void
      */
-    public function disable($watcherIdentifier);
+    public function disable($watcherId);
 
     /**
      * Cancel a watcher.
      *
-     * @param string $watcherIdentifier The watcher identifier.
+     * @param string $watcherId The watcher identifier.
      *
      * @return void
      */
-    public function cancel($watcherIdentifier);
+    public function cancel($watcherId);
 
     /**
      * Reference a watcher.
      *
      * This will keep the event loop alive whilst the event is still being monitored. Events have this state by default.
      *
-     * @param string $watcherIdentifier The watcher identifier.
+     * @param string $watcherId The watcher identifier.
      *
      * @return void
      */
-    public function reference($watcherIdentifier);
+    public function reference($watcherId);
 
     /**
      * Unreference a watcher.
      *
      * The event loop should exit the run method when only unreferenced events are still being monitored. Events are all
      * referenced by default.
      *
-     * @param string $watcherIdentifier The watcher identifier.
+     * @param string $watcherId The watcher identifier.
      *
      * @return void
      */
-    public function unreference($watcherIdentifier);
+    public function unreference($watcherId);
 
     /**
      * Check whether an optional features is supported by this implementation

Original file line number	Diff line number	Diff line change
`@@ -59,7 +59,7 @@ public static function stop()`
`59`	`59`	`/**`
`60`	`60`	`* Defer the execution of a callback.`
`61`	`61`	`*`
`62`		`- * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to defer.`
	`62`	`+ * @param callable(string $watcherId, mixed $data) $callback The callback to defer.`
`63`	`63`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`64`	`64`	`*`
`65`	`65`	`* @return string An identifier that can be used to cancel, enable or disable the watcher.`
`@@ -72,7 +72,7 @@ public static function defer(callable $callback, $data = null)`
`72`	`72`	`/**`
`73`	`73`	`* Delay the execution of a callback. The time delay is approximate and accuracy is not guaranteed.`
`74`	`74`	`*`
`75`		`- * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to delay.`
	`75`	`+ * @param callable(string $watcherId, mixed $data) $callback The callback to delay.`
`76`	`76`	`* @param int $time The amount of time, in milliseconds, to delay the execution for.`
`77`	`77`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`78`	`78`	`*`
`@@ -86,7 +86,7 @@ public static function delay(callable $callback, $time, $data = null)`
`86`	`86`	`/**`
`87`	`87`	`* Repeatedly execute a callback. The interval between executions is approximate and accuracy is not guaranteed.`
`88`	`88`	`*`
`89`		`- * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to repeat.`
	`89`	`+ * @param callable(string $watcherId, mixed $data) $callback The callback to repeat.`
`90`	`90`	`* @param int $interval The time interval, in milliseconds, to wait between executions.`
`91`	`91`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`92`	`92`	`*`
`@@ -101,7 +101,7 @@ public static function repeat(callable $callback, $interval, $data = null)`
`101`	`101`	`* Execute a callback when a stream resource becomes readable.`
`102`	`102`	`*`
`103`	`103`	`* @param resource $stream The stream to monitor.`
`104`		`- * @param callable(resource $stream, mixed $data, string $watcherIdentifier) $callback The callback to execute.`
	`104`	`+ * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.`
`105`	`105`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`106`	`106`	`*`
`107`	`107`	`* @return string An identifier that can be used to cancel, enable or disable the watcher.`
`@@ -115,7 +115,7 @@ public static function onReadable($stream, callable $callback, $data = null)`
`115`	`115`	`* Execute a callback when a stream resource becomes writable.`
`116`	`116`	`*`
`117`	`117`	`* @param resource $stream The stream to monitor.`
`118`		`- * @param callable(resource $stream, mixed $data, string $watcherIdentifier) $callback The callback to execute.`
	`118`	`+ * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.`
`119`	`119`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`120`	`120`	`*`
`121`	`121`	`* @return string An identifier that can be used to cancel, enable or disable the watcher.`
`@@ -129,7 +129,7 @@ public static function onWritable($stream, callable $callback, $data = null)`
`129`	`129`	`* Execute a callback when a signal is received.`
`130`	`130`	`*`
`131`	`131`	`* @param int $signo The signal number to monitor.`
`132`		`- * @param callable(int $signo, mixed $data, string $watcherIdentifier) $callback The callback to execute.`
	`132`	`+ * @param callable(string $watcherId, int $signo, mixed $data) $callback The callback to execute.`
`133`	`133`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`134`	`134`	`*`
`135`	`135`	`* @return string An identifier that can be used to cancel, enable or disable the watcher.`
`@@ -154,37 +154,37 @@ public static function onError(callable $callback)`
`154`	`154`	`/**`
`155`	`155`	`* Enable a watcher.`
`156`	`156`	`*`
`157`		`- * @param string $watcherIdentifier The watcher identifier.`
	`157`	`+ * @param string $watcherId The watcher identifier.`
`158`	`158`	`*`
`159`	`159`	`* @return void`
`160`	`160`	`*/`
`161`		`- public static function enable($watcherIdentifier)`
	`161`	`+ public static function enable($watcherId)`
`162`	`162`	`{`
`163`		`- self::get()->enable($watcherIdentifier);`
	`163`	`+ self::get()->enable($watcherId);`
`164`	`164`	`}`
`165`	`165`
`166`	`166`	`/**`
`167`	`167`	`* Disable a watcher.`
`168`	`168`	`*`
`169`		`- * @param string $watcherIdentifier The watcher identifier.`
	`169`	`+ * @param string $watcherId The watcher identifier.`
`170`	`170`	`*`
`171`	`171`	`* @return void`
`172`	`172`	`*/`
`173`		`- public static function disable($watcherIdentifier)`
	`173`	`+ public static function disable($watcherId)`
`174`	`174`	`{`
`175`		`- self::get()->disable($watcherIdentifier);`
	`175`	`+ self::get()->disable($watcherId);`
`176`	`176`	`}`
`177`	`177`
`178`	`178`	`/**`
`179`	`179`	`* Cancel a watcher.`
`180`	`180`	`*`
`181`		`- * @param string $watcherIdentifier The watcher identifier.`
	`181`	`+ * @param string $watcherId The watcher identifier.`
`182`	`182`	`*`
`183`	`183`	`* @return void`
`184`	`184`	`*/`
`185`		`- public static function cancel($watcherIdentifier)`
	`185`	`+ public static function cancel($watcherId)`
`186`	`186`	`{`
`187`		`- self::get()->cancel($watcherIdentifier);`
	`187`	`+ self::get()->cancel($watcherId);`
`188`	`188`	`}`
`189`	`189`
`190`	`190`	`/**`
`@@ -193,13 +193,13 @@ public static function cancel($watcherIdentifier)`
`193`	`193`	`* This will keep the event loop alive whilst the event is still being monitored. Watchers have this state by`
`194`	`194`	`* default.`
`195`	`195`	`*`
`196`		`- * @param string $watcherIdentifier The watcher identifier.`
	`196`	`+ * @param string $watcherId The watcher identifier.`
`197`	`197`	`*`
`198`	`198`	`* @return void`
`199`	`199`	`*/`
`200`		`- public static function reference($watcherIdentifier)`
	`200`	`+ public static function reference($watcherId)`
`201`	`201`	`{`
`202`		`- self::get()->reference($watcherIdentifier);`
	`202`	`+ self::get()->reference($watcherId);`
`203`	`203`	`}`
`204`	`204`
`205`	`205`	`/**`
`@@ -208,13 +208,13 @@ public static function reference($watcherIdentifier)`
`208`	`208`	`* The event loop should exit the run method when only unreferenced watchers are still being monitored. Events are`
`209`	`209`	`* all referenced by default.`
`210`	`210`	`*`
`211`		`- * @param string $watcherIdentifier The watcher identifier.`
	`211`	`+ * @param string $watcherId The watcher identifier.`
`212`	`212`	`*`
`213`	`213`	`* @return void`
`214`	`214`	`*/`
`215`		`- public static function unreference($watcherIdentifier)`
	`215`	`+ public static function unreference($watcherId)`
`216`	`216`	`{`
`217`		`- self::get()->unreference($watcherIdentifier);`
	`217`	`+ self::get()->unreference($watcherId);`
`218`	`218`	`}`
`219`	`219`
`220`	`220`	`/**`
Original file line number	Diff line number	Diff line change
`@@ -23,7 +23,7 @@ public function stop();`
`23`	`23`	`/**`
`24`	`24`	`* Defer the execution of a callback.`
`25`	`25`	`*`
`26`		`- * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to defer.`
	`26`	`+ * @param callable(string $watcherId, mixed $data) $callback The callback to defer.`
`27`	`27`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`28`	`28`	`*`
`29`	`29`	`* @return string An identifier that can be used to cancel, enable or disable the watcher.`
`@@ -33,7 +33,7 @@ public function defer(callable $callback, $data = null);`
`33`	`33`	`/**`
`34`	`34`	`* Delay the execution of a callback. The time delay is approximate and accuracy is not guaranteed.`
`35`	`35`	`*`
`36`		`- * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to delay.`
	`36`	`+ * @param callable(string $watcherId, mixed $data) $callback The callback to delay.`
`37`	`37`	`* @param int $delay The amount of time, in milliseconds, to delay the execution for.`
`38`	`38`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`39`	`39`	`*`
`@@ -44,7 +44,7 @@ public function delay(callable $callback, $delay, $data = null);`
`44`	`44`	`/**`
`45`	`45`	`* Repeatedly execute a callback. The interval between executions is approximate and accuracy is not guaranteed.`
`46`	`46`	`*`
`47`		`- * @param callable(mixed $data, string $watcherIdentifier) $callback The callback to repeat.`
	`47`	`+ * @param callable(string $watcherId, mixed $data) $callback The callback to repeat.`
`48`	`48`	`* @param int $interval The time interval, in milliseconds, to wait between executions.`
`49`	`49`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`50`	`50`	`*`
`@@ -56,7 +56,7 @@ public function repeat(callable $callback, $interval, $data = null);`
`56`	`56`	`* Execute a callback when a stream resource becomes readable.`
`57`	`57`	`*`
`58`	`58`	`* @param resource $stream The stream to monitor.`
`59`		`- * @param callable(resource $stream, mixed $data, string $watcherIdentifier) $callback The callback to execute.`
	`59`	`+ * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.`
`60`	`60`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`61`	`61`	`*`
`62`	`62`	`* @return string An identifier that can be used to cancel, enable or disable the watcher.`
`@@ -67,7 +67,7 @@ public function onReadable($stream, callable $callback, $data = null);`
`67`	`67`	`* Execute a callback when a stream resource becomes writable.`
`68`	`68`	`*`
`69`	`69`	`* @param resource $stream The stream to monitor.`
`70`		`- * @param callable(resource $stream, mixed $data, string $watcherIdentifier) $callback The callback to execute.`
	`70`	`+ * @param callable(string $watcherId, resource $stream, mixed $data) $callback The callback to execute.`
`71`	`71`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`72`	`72`	`*`
`73`	`73`	`* @return string An identifier that can be used to cancel, enable or disable the watcher.`
`@@ -78,7 +78,7 @@ public function onWritable($stream, callable $callback, $data = null);`
`78`	`78`	`* Execute a callback when a signal is received.`
`79`	`79`	`*`
`80`	`80`	`* @param int $signo The signal number to monitor.`
`81`		`- * @param callable(int $signo, mixed $data, string $watcherIdentifier) $callback The callback to execute.`
	`81`	`+ * @param callable(string $watcherId, int $signo, mixed $data) $callback The callback to execute.`
`82`	`82`	`* @param mixed $data Arbitrary data given to the callback function as the $data parameter.`
`83`	`83`	`*`
`84`	`84`	`* @return string An identifier that can be used to cancel, enable or disable the watcher.`
`@@ -97,52 +97,52 @@ public function onError(callable $callback);`
`97`	`97`	`/**`
`98`	`98`	`* Enable a watcher.`
`99`	`99`	`*`
`100`		`- * @param string $watcherIdentifier The watcher identifier.`
	`100`	`+ * @param string $watcherId The watcher identifier.`
`101`	`101`	`*`
`102`	`102`	`* @return void`
`103`	`103`	`*/`
`104`		`- public function enable($watcherIdentifier);`
	`104`	`+ public function enable($watcherId);`
`105`	`105`
`106`	`106`	`/**`
`107`	`107`	`* Disable a watcher.`
`108`	`108`	`*`
`109`		`- * @param string $watcherIdentifier The watcher identifier.`
	`109`	`+ * @param string $watcherId The watcher identifier.`
`110`	`110`	`*`
`111`	`111`	`* @return void`
`112`	`112`	`*/`
`113`		`- public function disable($watcherIdentifier);`
	`113`	`+ public function disable($watcherId);`
`114`	`114`
`115`	`115`	`/**`
`116`	`116`	`* Cancel a watcher.`
`117`	`117`	`*`
`118`		`- * @param string $watcherIdentifier The watcher identifier.`
	`118`	`+ * @param string $watcherId The watcher identifier.`
`119`	`119`	`*`
`120`	`120`	`* @return void`
`121`	`121`	`*/`
`122`		`- public function cancel($watcherIdentifier);`
	`122`	`+ public function cancel($watcherId);`
`123`	`123`
`124`	`124`	`/**`
`125`	`125`	`* Reference a watcher.`
`126`	`126`	`*`
`127`	`127`	`* This will keep the event loop alive whilst the event is still being monitored. Events have this state by default.`
`128`	`128`	`*`
`129`		`- * @param string $watcherIdentifier The watcher identifier.`
	`129`	`+ * @param string $watcherId The watcher identifier.`
`130`	`130`	`*`
`131`	`131`	`* @return void`
`132`	`132`	`*/`
`133`		`- public function reference($watcherIdentifier);`
	`133`	`+ public function reference($watcherId);`
`134`	`134`
`135`	`135`	`/**`
`136`	`136`	`* Unreference a watcher.`
`137`	`137`	`*`
`138`	`138`	`* The event loop should exit the run method when only unreferenced events are still being monitored. Events are all`
`139`	`139`	`* referenced by default.`
`140`	`140`	`*`
`141`		`- * @param string $watcherIdentifier The watcher identifier.`
	`141`	`+ * @param string $watcherId The watcher identifier.`
`142`	`142`	`*`
`143`	`143`	`* @return void`
`144`	`144`	`*/`
`145`		`- public function unreference($watcherIdentifier);`
	`145`	`+ public function unreference($watcherId);`
`146`	`146`
`147`	`147`	`/**`
`148`	`148`	`* Check whether an optional features is supported by this implementation`