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To: PHP Developers Mailing List <internals@lists.php.net>
Thread-Topic: Putting the match expression in constant expressions in PHP 8.0
 or 8.1
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Date: Sat, 8 Aug 2020 00:21:58 +0000
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Subject: Putting the match expression in constant expressions in PHP 8.0 or
 8.1
From: tysonandre775@hotmail.com (tyson andre)

Hi internals,=0A=
=0A=
The match expression can be thought of as a much more concise/readable equi=
valent to chained ternary operators.=0A=
I'm proposing allowing matches in constant expressions when all parts of th=
e match are constant expressions.=0A=
=0A=
For example, these two class constants would have equivalent behaviors if m=
atch expressions were allowed in constant expressions.=0A=
=0A=
```=0A=
class MyClass {=0A=
    const CONFIG_SETTING =3D (APP_ENVIRONMENT =3D=3D 'dev' || APP_ENVIRONME=
NT =3D=3D 'stage') ? 'development-config' :=0A=
        (APP_ENVIRONMENT =3D=3D 'prod' ? 'production-config' : null);=0A=
=0A=
    const CONFIG_SETTING =3D match(APP_ENVIRONMENT) {=0A=
        'dev', 'stage' =3D> 'development-config',=0A=
        'prod' =3D> 'production-config',=0A=
        default =3D> null,=0A=
    };=0A=
}=0A=
```=0A=
=0A=
https://github.com/php/php-src/pull/5951 implements the main part of the ch=
ange.=0A=
=0A=
This is mostly for the sake of consistency, since match can be thought of a=
s yet another control flow primitive that is more readable under some circu=
mstances.=0A=
=0A=
So I had some questions:=0A=
1. Should this target 8.0 or 8.1? I'm leaning towards 8.1 since the beta is=
 already out.=0A=
2. Are there objections to doing this?=0A=
3. Should/shouldn't php enforce that the default arm exists for match *in c=
onstant expressions*=0A=
   (constant expressions can already throw errors when evaluated for variou=
s reasons, but UnhandledMatchError is new)=0A=
=0A=
Thanks,=0A=
- Tyson=