output.txt

$ php test.php
PHP Fatal error:  Uncaught TypeError: Return value of doStuff() must be of the type bool, int returned in test.php:10
Stack trace:
#0 test.php(13): doStuff()
#1 {main}
  thrown in test.php on line 10

Fatal error: Uncaught TypeError: Return value of doStuff() must be of the type bool, int returned in test.php:10
Stack trace:
#0 test.php(13): doStuff()
#1 {main}
  thrown in test.php on line 10

test.php

<?php
declare(strict_types=1);

function gimmeTrue(): bool { return true; }

function doStuff(): bool
{
	$success = gimmeTrue();
	$success &= gimmeTrue();
	return $success;
}

doStuff();