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Date: Tue, 3 Jun 2025 22:01:22 +0300
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Subject: Re: [PHP-DEV] [RFC] Transform void into an alias for null
To: "Gina P. Banyard" <internals@gpb.moe>
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From: sandfox@sandfox.me (Anton Smirnov)

On 03/06/2025 18:20, Gina P. Banyard wrote:
> On Tuesday, 3 June 2025 at 02:36, Anton Smirnov <sandfox@sandfox.me> wrote:
> 
>> On 02/06/2025 23:50, Rowan Tommins [IMSoP] wrote:
>>
>>> I agree the type hierarchy you describe is weird, but rather than
>>> throwing away the functionality completely, I wonder if we can make it
>>> more consistent:
>>>
>>> - Make "no return type declared" and "mixed" equivalent
>>> - Make "void" a sub-type of "null", and therefore a sub-type of "mixed"
>>
>>
>> I think that null and void are semantically very different so I'd like
>> to suggest just making void subtype of mixed. This will both keep the
>> semantic meaning of void and make mixed and undeclared mean the same thing.
> 
> You are going to need to expand on why you think those two are semantically very different.
> PHP does not have the concept of "execution control is returned to the calling scope, but no concrete value is returned".
> And this is a good thing IMHO, as it means you can always take the result of a function.

Basically I agree with Ilija and Tim that functions that "return null" 
and functions that "return nothing but it's shown as null for historical 
and compatibility reasons" are different, but I see some value in 
aligning mixed and undeclared return type behavior.

> Moreover, "just making void subtype of mixed" can mean everything and nothing.
> Do you mean for void to live on its own island like the int or string types?
> Make it a subtype of null like Roman suggested?
> Have void be a super type of some weird union of types representing scalars int|string|float|bool?
> Something else altogether?

this:

 > Do you mean for void to live on its own island like the int or string 
types?

never <- void <- mixed

-- 
Anton