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Date: Thu, 25 May 2017 19:38:08 +0300
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To: Marco Pivetta <ocramius@gmail.com>
Cc: "internals@lists.php.net" <internals@lists.php.net>, Rasmus Schultz <rasmus@mindplay.dk>
Content-Type: text/plain; charset="UTF-8"
Subject: Re: [PHP-DEV] Parameter type widening RFC
From: narf@devilix.net (Andrey Andreev)

Hi Marco,

On Thu, May 25, 2017 at 6:58 PM, Marco Pivetta <ocramius@gmail.com> wrote:
> On Thu, May 25, 2017 at 4:30 PM, Andrey Andreev <narf@devilix.net> wrote:
>>
>> I'm trying, but fail to find a source that says replacing stdClass
>> with mixed/any/etc is ok.
>
>
> It is OK for a subtype to handle a wider range of types than its contract,
> it is not ok for the subtype to handle a smaller range of types than its
> contract.
>
> A contract says what you "must" be able to do to satisfy it, so the
> invariants hold.
>

Sorry, but by "source" I didn't mean somebody state it here. :)

When I said I don't claim to fully understand LSP, I didn't mean "tell
me what it is" - I'm familiar with it. What I don't understand is how
do we get from this:

> Wikipedia:
>
> an object of type T may be substituted with any object of a subtype S


To this:

> A single type may be substituted by any other type


Cheers,
Andrey.