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Date: Fri, 22 Apr 2016 08:39:36 -0600
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To: Jordi Boggiano <j.boggiano@seld.be>
Cc: internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV][RFC] Callable Types
From: levim@php.net (Levi Morrison)

> Not much else to say, the syntax reads a bit weird/heavy being all in-line
> with the function signature but at the same time I can't imagine how else it
> would work that would be any better.

As mentioned on Reddit and in the future scope section of union types,
we may want to introduce named type expressions:

    type IntReducer = callable(int, int): int;

Which would also allow unions (if passed, of course):

    type Iterable = Array | Traversable;

It would also allow for a general type-aliasing mechanism for single
names. This feature has been asked for in the past but I can't
remember the use-cases so this example is not very good:

    type Foo = SomeFoo;

Then we just use the names where we would have put the expressions:

    function reduce(int $a, int $b, IntReducer $reducer): int {
        return $reducer($a, $b);
    }