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Date: Thu, 19 Mar 2020 23:10:02 +0100
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Thread-Topic: [RFC] throw expression
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Subject: [RFC] throw expression
From: ilija.tovilo@me.com (Ilija Tovilo)

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Hi everybody!

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Yesterday I stumbled upon this Tweet by Nikita:

https://twitter.com/nikita_ppv/status/1240309838950866946

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It answered why this seemingly correct block of code doesn't work:

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=C2=A0=C2=A0=C2=A0 fn() =3D> throw new Exception('nope');

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The answer is rather simple. `throw` is a statement, not an expression. How=
ever, arrow functions only allow a single expression as their bodies. The ob=
vious solution is to convert `throw` to an expression. This would also allow=
 for the following:

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=C2=A0=C2=A0=C2=A0 $value =3D $nullableValue ?? throw new InvalidArgumentException();

=C2=A0=C2=A0=C2=A0 $value =3D $falsableValue ?: throw new InvalidArgumentException();

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At the moment this is generally done by moving the `throw` into a function:

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=C2=A0=C2=A0=C2=A0 function throwInvalidArgumentException() {

=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 throw new InvalidArgumentException();

=C2=A0=C2=A0=C2=A0 }

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=C2=A0=C2=A0=C2=A0 $value =3D $nullableValue ?? throwInvalidArgumentException();

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or of course by just using an `if` statement:

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=C2=A0=C2=A0=C2=A0 if ($nullableValue =3D=3D=3D null) {

=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0throw new InvalidArgumentException();

=C2=A0=C2=A0=C2=A0 }

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Neither of those are bad. The new syntax is just slightly more concise.

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An implementation of the change can be found here:

https://github.com/php/php-src/pull/5279

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It's also noteworthy that the same feature has semi-recently been added to =
C# 7.0:

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/=
throw#the-throw-expression

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This has been proposed a handful of times in the internals mailing list but=
 never extensively discussed:

https://externals.io/message/49569 (2010)

https://externals.io/message/15301 (2005)

https://externals.io/message/10553 (2004)

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Let me know what you think!

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Also, to actually create the RFC I need RFC karma. Can someone grant me tho=
se privileges? My username is ilijatovilo.

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Thank you!


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