Eloquent\Phony\Hook\FunctionHookManager::defineFunction PHP Method

    public function defineFunction($name, $namespace, $callback)
    {
        $signature = $this->signatureInspector->callbackSignature($callback);
        $fullName = $namespace . '\\' . $name;
        $key = strtolower($fullName);
        if (isset(self::$hooks[$key])) {
            if ($signature !== self::$hooks[$key]['signature']) {
                throw new FunctionSignatureMismatchException($fullName);
            }
            $replaced = self::$hooks[$key]['callback'];
        } else {
            $replaced = null;
            if (function_exists($fullName)) {
                throw new FunctionExistsException($fullName);
            }
            $source = $this->hookGenerator->generateHook($name, $namespace, $signature);
            $reporting = error_reporting(E_ERROR | E_COMPILE_ERROR);
            $error = null;
            try {
                eval($source);
            } catch (ParseError $e) {
                $error = new FunctionHookGenerationFailedException($fullName, $callback, $source, error_get_last(), $e);
                // @codeCoverageIgnoreStart
            } catch (ParseException $e) {
                $error = new FunctionHookGenerationFailedException($fullName, $callback, $source, error_get_last(), $e);
            } catch (Throwable $error) {
                // re-thrown after cleanup
            } catch (Exception $error) {
                // re-thrown after cleanup
            }
            // @codeCoverageIgnoreEnd
            error_reporting($reporting);
            if ($error) {
                throw $error;
            }
            if (!function_exists($fullName)) {
                // @codeCoverageIgnoreStart
                throw new FunctionHookGenerationFailedException($fullName, $callback, $source, error_get_last());
                // @codeCoverageIgnoreEnd
            }
        }
        self::$hooks[$key] = array('callback' => $callback, 'signature' => $signature);
        return $replaced;
    }