Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:93741
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain gmail.com designates 74.125.82.41 as permitted sender)
References: <BLU437-SMTP785CB095BE08FBC1CC2FAFE2580@phx.gbl>
 <0A.C5.62101.1C860575@pb1.pair.com>
 <a58caf44-dae1-c544-804f-089360243607@gmail.com>
 <BLU436-SMTP187447B1819635CD2E6962E2580@phx.gbl>
 <68b821ac-d71f-4be5-8dca-ae94db332630@gmail.com>
 <BLU436-SMTP208CF2757B67BA061C8EEADE2580@phx.gbl>
 <20160603101659.D466A1A81FC5@dd1730.kasserver.com>
To: internals@lists.php.net
Message-ID: <6d448fd8-8fda-d795-accb-6b96cd128ccd@gmail.com>
Date: Fri, 3 Jun 2016 11:28:04 +0100
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101
 Thunderbird/45.1.1
MIME-Version: 1.0
In-Reply-To: <20160603101659.D466A1A81FC5@dd1730.kasserver.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [PHP-DEV] Re: [RFC] [PRE-VOTE] Union types
From: rowan.collins@gmail.com (Rowan Collins)

On 03/06/2016 11:16, Thomas Bley wrote:
> why not try all types weakly from left to right in weak mode?
> Rule: if type check would give a fatal error for a type, try next type.

This is what I suggested, but Bob is insistent that weak mode should 
always select the same type as strict mode where there is a valid strict 
match, which I guess makes sense.

A strict left-to-right check violates that:

function i(string | int $x) { echo gettype($x); }
i(10); // string in weak mode, int in strict mode

function j(int | string $x) { echo gettype($x); }
j('10'); // int in weak mode, string in strict mode


The main complication that I haven't quite got my head round yet is the 
fact that an int->float coercion is allowed in strict mode. So to be 
consistent, weak mode needs to privilege that cast:

function k(string | float $x) { echo gettype($x); }
k(10); // float

But in other cases it doesn't seem sensible to privilege float over string:

function l(string | float $x) { echo gettype($x); }
l("1.5a"); // I would expect string, but float would succeed if attempted

Regards,
-- 
Rowan Collins
[IMSoP]