Online PHP editor | output for 93YM6

<?php interface FormStateInterface {} class FormState implements FormStateInterface {} class Config {} class ConfigFormBase { public function submitForm(array &$form, FormStateInterface $form_state) { var_dump(method_exists($this, 'mapFormValuesToConfig')); } } trait ValidatableConfigFormTrait { abstract protected static function mapFormValuesToConfig(FormStateInterface $form_state, Config $config): void; } class MyForm extends ConfigFormBase { use ValidatableConfigFormTrait; protected static function mapFormValuesToConfig(FormStateInterface $form_state, Config $config): void { // without this, PHP will complain! 👍 } } class SubMyForm extends MyForm {} $form = []; (new MyForm())->submitForm($form, new FormState()); (new SubMyForm())->submitForm($form, new FormState());