Finally! I had a lot of concerns about this, but I think they're mostly answered by the discussion. I do like the way union types work (at least nullable types) in Hack, but I think they existing `foo(int $param = null)` approach is fine for 99% of cases, and those that it doesn't work for can go back to type-checking at the top of the function (ie do what we have to do for all scalar types right now).
While I understand the optional strict mode, I do find it quite confusing: it looks similar to javascript's 'use strict';, and at first glance it sounds like it should be similar to `error_reporting(E_STRICT)`, yet somehow scoped to the <?php ?>. Personally I like the `strict namespace` approach they proposed the most. The argument against is that it will read like everything in that namespace is strict, when it's actually limited to the file, but I think it's pretty clear if I read in a.php `strict namespace Qaribou;` and in b.php `namespace Qaribou;`, that a.php is strict and b.php is not. I really don't see the ambiguity there.
While I understand the optional strict mode, I do find it quite confusing: it looks similar to javascript's 'use strict';, and at first glance it sounds like it should be similar to `error_reporting(E_STRICT)`, yet somehow scoped to the <?php ?>. Personally I like the `strict namespace` approach they proposed the most. The argument against is that it will read like everything in that namespace is strict, when it's actually limited to the file, but I think it's pretty clear if I read in a.php `strict namespace Qaribou;` and in b.php `namespace Qaribou;`, that a.php is strict and b.php is not. I really don't see the ambiguity there.