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Date: Thu, 14 Apr 2016 20:33:41 -0400
To: Levi Morrison <levim@php.net>
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Thread-Topic: [PHP-DEV] [RFC] Nullable Return Type Declaration
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Subject: Re: [PHP-DEV] [RFC] Nullable Return Type Declaration
From: fsb@thefsb.org (Tom Worster)

On 4/14/16, 5:46 PM, "Levi Morrison" <morrison.levi@gmail.com on behalf of
levim@php.net> wrote:

>Having a separate method instead of `foo(null, "value")` makes it
>difficult to use for the result of a function.

I suspect that might be a good thing:) I don't know for sure but the
possibility exists.


>Assume `bar()` returns
>`Bar | Null`; this would no longer work if they were separated:
>
>    foo(bar(), "value")
>
>Functions are often composed so if something is the output of one
>function it will likely be the input to another. Thus if returning
>optionally null values is important to you so should optionally null
>parameters.

This was a chin-scratcher for me. On one hand, I see what you mean. On the
other I couldn't think of an example from my experience (which I admit is
very narrow -- I live a sheltered life) of such a bar() that I would feed
straight foo().

The semantic convention for Something or null return, as I see it, is when
bar() returns null, it is saying "I got nothing". What kind of foo() does
the same thing to nothing at all as it does to a Something object? This is
where I got stuck.

Say I was doing the composition instead via chaining.
Something::bar()->foo("value") is nonsense if bar() could return null.
This suggests to me that the other composition might not be wise.

*Either* bar() should not be returning Something or null (maybe it should
instead return some other type that can represent all the possible
returns) *or* we shouldn't try to compose like this and should test for
the Somethingness of bar()'s return before apply ->foo("value") or foo(=E2=80=A6,
"value") to it. Or maybe this API needs an even more fundamental redesign.

So, from my perspective, this might be an example of the limitation
nudging us to think harder about the design.

Tom