[Proposal]: simplify testing multiple equality with in comparison

[softlion]

In comparison

• Proposed
• Prototype: Not Started
• Implementation: Not Started
• Specification: Not Started

Summary

This code:

IsRotating = args.Status == GestureStatus.Started ||  args.Status == GestureStatus.Running

could be simplified to:

IsRotating = args.Status in [GestureStatus.Started, GestureStatus.Running]

like in the SQL language.

Motivation

Cleaner code with all the benefits by stopping repeating the equality comparison and the first argument to this comparison.

Detailed design

This could be expanded by the compiler into the original syntax.

Drawbacks

"in" is a new keyword there. But it should not impact the existing syntaxes.

Alternatives

None ?

Unresolved questions

In this the correct keyword to use ?

Design meetings

[svick]

C# 9.0 includes or patterns, which allow you to write code like the following:

IsRotating = args.Status is GestureStatus.Started or GestureStatus.Running;

Is that sufficient for your needs?

[softlion]

This syntax is not good. Because « as » is used to compare to a type, not to the value in one type. And because « or » is not the normal or operator.

This makes this syntax bad, badly discoverable and badly understandable, while adding complexity for beginners.

I liked most of your changes.
But for c#9 you are all wrong there guys.

[CyrusNajmabadi]

that same argument applies to your syntax. in already means something else in c#. As does [] in an expression context.

Los of c# syntax is reused in different places to mean different things. That's ok and is a standard part of the language. You're doing that yourself with your proposal. :-)

[theunrepentantgeek]

@softlion the is and as operators were extended in C# 8 into pattern operators, and in C# 9 they can test for patterns involving values as well. They are no longer merely doing type comparisons. The syntax shown by @svick is already available in preview, and is on track to be generally released within weeks.