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Date: Thu, 14 Apr 2016 08:27:25 -0600
Message-ID: <CAFMT4NoDvfkP6VL8So24Jua-XiLFnmmGOUpNLFWM3D2Xf3JtLA@mail.gmail.com>
To: Davey Shafik <davey@php.net>
Cc: Derick Rethans <derick@php.net>, Lin Yo-An <cornelius.howl@gmail.com>, 
	internals <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] [RFC] Union Types
From: morrison.levi@gmail.com (Levi Morrison)

> Also, just to clarify, if you combine this with the nullable types syntax
> (assuming prefix), then the nullable applies to the entire union type:
>
> ?int|float === int | float | null
>
> I do find the shorter syntax confusing TBH.
>
> Which actually leads me to a different thought: defining custom types and
> using them instead.
>
> I very much like Hacks type/newtype stuff, if we extended that to support
> union types:
>
> newtype Numeric = int|float;
>
> Then you end up with simply: ?Numeric as your type (it should be
> namespaced).
>
> You could further expand that with casting rules:
>
> newtype Numeric = int|float {
>       string as float;
>       bool as int;
> }
>
> or even go so far as:
>
> newtype Numeric = function($value): int|float {
>      if ($value typeof int) {
>          return $value;
>      }
>
>     return (float) $value;
> }
>
> FTR: I hate that last one, just spitballing.
>
> - Davey
>
> P.S.
> if someone is willing to tackle the code for custom types I'm willing to
> write an RFC

This issue is addressed partially in the future scope section of the
RFC: https://wiki.php.net/rfc/union_types#long_type_expressions.

If both nullable and full union types are allowed I was planning on
disallowing the short-hand notation when using unions. As it isn't
that relevant at this stage it isn't noted in the RFCs anywhere.