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Date: Fri, 26 May 2017 18:16:45 +0200
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Subject: Re: [PHP-DEV] Parameter type widening RFC
From: lists@rhsoft.net ("lists@rhsoft.net")



Am 26.05.2017 um 18:10 schrieb Ryan Pallas:
> 
> 
> On Fri, May 26, 2017 at 9:01 AM, lists@rhsoft.net 
> <mailto:lists@rhsoft.net> <lists@rhsoft.net <mailto:lists@rhsoft.net>> 
> wrote:
> 
> 
> 
>     Am 26.05.2017 um 16:26 schrieb Dan Ackroyd:
> 
>         On 26 May 2017 at 13:23, lists@rhsoft.net
>         <mailto:lists@rhsoft.net> <lists@rhsoft.net
>         <mailto:lists@rhsoft.net>> wrote:
> 
>             does that also fix the issue
>             https://bugs.php.net/bug.php?id=74394
>             <https://bugs.php.net/bug.php?id=74394>
> 
> 
>         Dear Anonymous,
> 
>         That "issue" is actually 3 issues.
> 
>         case 1
> 
>         class A {
>             public function test($a) {}
>         }
>         class B extends A {
>             public function test(string $a) { }
>         }
> 
>         This breaks LSP - because B::test doesn't accept all the things that
>         A::test can accept and so is unlikely to ever be supported.
> 
> 
>     and how is that a problem?
> 
>     A accepts anything
>     B limits it's inut to a *subset* of "anything"
> 
> Because, if I have a function foo(A $a) { $a->test(new Bar()) } that I 
> cannot pass B into this function, even though it is a subclass of A. You 
> should be able to pass any subclass where its parent is expected, 
> allowing parameter narrowing (covariance) would break this.

well, that case is at least a warning

but add a return-type to the parent is a *fatal error* until you update 
the child class and that makes introducing return-types harder than it 
should be

something like "covariance class {}" would be xtremely helpful for all 
that cases where you don't pass objects all day around but have them as 
a *library* in a singletone - in such cases there is no technical 
difference when you add a retrun-type to the parent class then before 
except that what was over years just a "@return integer" is now instead 
of a comment a language construct