source/Core/Registry.php
public static function instanceExists($className)
    {
        $key = self::getStorageKey($className);

        return isset(self::$instances[$key]);
    }
public static function instanceExists($className)
    {
        $key = self::getStorageKey($className);

        return isset(self::$instances[$key]);
    }
public static function instanceExists ( $ className ) { $ key = self :: getStorageKey ( $ className ) ; return isset ( self :: $ instances [ $ key ] ) ; }
Check if an instance of a given class is set in the registry

@param string $className

@return bool
Check if an instance of a given class is set in the registry