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Date: Fri, 18 Dec 2020 20:40:24 +0100
Message-ID: <CAJpLVh1KA8_Tqh28xrvX0CamYaSSmyQLMN3xTrwXZEJqN+G7kQ@mail.gmail.com>
To: Larry Garfield <larry@garfieldtech.com>
Cc: php internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="0000000000005d539a05b6c24894"
Subject: Re: [PHP-DEV] [RFC] Short-match
From: olleharstedt@gmail.com (=?UTF-8?Q?Olle_H=C3=A4rstedt?=)

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What about matching on a variable's type?

```
match {
  $var: string => "is a string"
  $var: array => "something else"
}
```

This could be used with flow-sensitive typing, e.g. assume the type of $var
being string in the string block. Psalm works like this for if-statements.
Also consider the case with generics.

Compare with generalised algebraic data types in FP (GADT).

Olle

On Thu, 17 Dec 2020, 22:01 Larry Garfield, <larry@garfieldtech.com> wrote:

> On Thu, Dec 17, 2020, at 10:23 AM, Sara Golemon wrote:
> > On Wed, Dec 16, 2020 at 6:50 PM someniatko <someniatko@gmail.com> wrote:
> > >
> > > `match` is an expression, where as if-else construction is not. This
> > > allows for combining it with a potential future feature of single line
> > > functions and methods. For example (hypothetical syntax is used):
> > >
> > > ```
> > > $getNumber = fn(int $number) => match {
> > >     $number < 0 => NumberKind::NEGATIVE,
> > >     $number == 0 => NumberKind::ZERO,
> > >     $number > 0 => NumberKind::POSITIVE,
> > > };
> > > ```
> > >
> >
> > That does read attractively, yes.  This is the example that should have
> > been offered first as it shows the expression nature shining.
> >
> > To contrast that with what would be possible now in an expressive
> > functional form:
> >
> > $getNumber = fn(int $number) => [
> >   -1 => NumberKind::NEGATIVE,
> >   0 => NumberKind::ZERO,
> >   1 => NumberKind::POSITIVE,
> > ][$number <=> 0];
> >
> > The match form *certainly* reads more naturally than the spaceship
> indexing
> > form even though both take up equal space.
> >
> > -Sara
>
> It looks like the quoted part from someniatko changed from a named
> function to an anon function?  Not sure what happened there.
>
> I've included both a named and lambda version of his example in the RFC,
> however, and linked to the short-functions RFC as that would allow the form
> he originally listed.  They complement each other nicely.
>
> --Larry Garfield
>
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