lib/Twig/lib/Twig/Environment.php
public function hasExtension($class)
    {
        $class = ltrim($class, '\\');
        if (!isset($this->extensionsByClass[$class]) && class_exists($class, false)) {
            // For BC/FC with namespaced aliases
            $class = new ReflectionClass($class);
            $class = $class->name;
        }

        if (isset($this->extensions[$class])) {
            if ($class !== get_class($this->extensions[$class])) {
                @trigger_error(sprintf('Referencing the "%s" extension by its name (defined by getName()) is deprecated since 1.26 and will be removed in Twig 2.0. Use the Fully Qualified Extension Class Name instead.', $class), E_USER_DEPRECATED);
            }

            return true;
        }

        return isset($this->extensionsByClass[$class]);
    }
public function hasExtension($class)
    {
        $class = ltrim($class, '\\');
        if (!isset($this->extensionsByClass[$class]) && class_exists($class, false)) {
            // For BC/FC with namespaced aliases
            $class = new ReflectionClass($class);
            $class = $class->name;
        }

        if (isset($this->extensions[$class])) {
            if ($class !== get_class($this->extensions[$class])) {
                @trigger_error(sprintf('Referencing the "%s" extension by its name (defined by getName()) is deprecated since 1.26 and will be removed in Twig 2.0. Use the Fully Qualified Extension Class Name instead.', $class), E_USER_DEPRECATED);
            }

            return true;
        }

        return isset($this->extensionsByClass[$class]);
    }
public function hasExtension ( $ class ) { $ class = ltrim ( $ class , '\\' ) ; if ( ! isset ( $ this -> extensionsByClass [ $ class ] ) && class_exists ( $ class , false ) ) { // For BC/FC with namespaced aliases $ class = new ReflectionClass ( $ class ) ; $ class = $ class -> name ; } if ( isset ( $ this -> extensions [ $ class ] ) ) { if ( $ class !== get_class ( $ this -> extensions [ $ class ] ) ) { @ trigger_error ( sprintf ( 'Referencing the "%s" extension by its name (defined by getName()) is deprecated since 1.26 and will be removed in Twig 2.0. Use the Fully Qualified Extension Class Name instead.' , $ class ) , E_USER_DEPRECATED ) ; } return true ; } return isset ( $ this -> extensionsByClass [ $ class ] ) ; }
Returns true if the given extension is registered.

@param string $class The extension class name

@return bool Whether the extension is registered or not
Returns true if the given extension is registered .