TIL you cannot give PHP's scalar typehints any default value other than `null`. Completely with a misleading error message.

example.php

<?php

function foo(boolean $hello=true)
{
  // ...
}

/*
local> php -l example.php 
PHP Fatal error:  Default value for parameters with a class type hint can only be NULL in t.php on line 3

Fatal error: Default value for parameters with a class type hint can only be NULL in t.php on line 3

Errors parsing example.php
*/

Use bool, not boolean. Aliases are not supported. See the original RFC: https://wiki.php.net/rfc/scalar_type_hints_v5

Thanks @jasonlotito!

https://3v4l.org/OiNiO <- still fails on HHVM but that's another issue 👍