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Message-ID: <570FF045.1040307@seld.be>
Date: Thu, 14 Apr 2016 20:32:21 +0100
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Subject: Re: [PHP-DEV] Re: Improving PHP's type system
From: j.boggiano@seld.be (Jordi Boggiano)

Heya,

On 14/04/2016 19:59, Stanislav Malyshev wrote:
>> I don't know what is complicated about "string|Stringable" or "Foo|Bar"
>> since it is super self-explanatory. However, I find myself checking the
>
> It may be self-explanatory for you. It's much less self-explanatory for
> somebody just starting to learn. It is also very dangerous - if it's
> either Foo or Bar, can you call Foo::stuff on it or not? If it's string
> or not string, can you call strlen on it? Etc., etc. It adds a lot of
> cognitive load and complicates the whole picture.

I don't really think it's much more complex to grasp `Foo|Bar $foo` than 
only `Foo $foo`. I mean once you grasp the concept of type hints you 
probably have by then a good understanding of || and hopefully can 
derive understanding from there.

That said I agree it's rarely useful, and as such I am not expecting 
we'll see this all over the place, it's just nice to have when you need 
it, but I can't think of very many valid cases (nullable types are much 
more common).

Please take that into consideration as well when arguing that it adds 
complexity. If it's rarely seen in the wild it's not very valuable but 
it's *also* not hindering newcomers often.

> You may have a
> specific use case where it is useful (which we have yet to see btw) but
> please remember it's a language with literally millions of use cases and
> users.

Just to highlight one use case I can think of, here is one:

https://github.com/Seldaek/monolog/blob/master/src/Monolog/Handler/MongoDBHandler.php#L51-L53

We need some sort of Mongo thing, and there are two available with 
different interfaces, so here both are accepted but as you see in the 
code below they are handled kinda separately. It would just save us 
those 3 lines of check if we could type-hint appropriately.

And it would save us one line of phpdoc as well because IDEs could infer 
the information from the code.

Cheers

-- 
Jordi Boggiano
@seldaek - http://seld.be