Discussion: reference equality operator

[alrz]

dotnet/roslyn#8409 suggests to use === and !== operators as the reference equality operator. Although, since is null covered half of the use cases, is it possible to use the same operator to do a reference equality check with a generic expression?

var equal = e1 is e2;

[DavidArno]

I think your is syntax:

var equal = e1 is e2;

is a huge improvement on ===, as I suspect anyone who's been near JavaScript, reads the latter as "really equal" or similar.

[orthoxerox]

So e1 is e2 is literally ReferenceEquals(e1, e2)? Are there that many cases when you must test your objects for reference equality, but their == operator is overridden to mean something different?

[alrz]

As it turns out ReferenceEquals call, already generates optimized code. Closing.

[jnm2]

Please reopen? The main benefit I was looking forward to was replacing all my ReferenceEquals(x, y) with x is y syntax!

[DavidArno]

Seconding @jnm2: I thought the whole point to this proposal was for better syntax for object.ReferenceEquals(x, y). I'd expect the bytecode to be identical, so don't see this as a performance issue.

[alrz]

The first issue that arises here is that it silently changes the semantics of is based on RHS being a pattern (or active pattern) or not.

[dstarkowski]

Won't this conflict with current is operator?

String String = "a";
String Other = "a";
var equal = Other is String;

[alrz]

No binding changes are suggested as part of this proposal. You could already use is (String) to force it to be resolved as an expression.

[YaakovDavis]

The main benefit I was looking forward to was replacing all my ReferenceEquals(x, y) with x is y syntax

I would disagree that x is y is beneficiary over ReferenceEquals(x, y). The latter is explicit, while the former is vague. With all pattern matching going around, one will have to remember what is means in this case.

Related to that, there were multiple proposals of allowing the user to reinterpret is. This proposal conflicts with those.

I'd rather have flexibility over is reinterpretation, than a hardcoded "reference equality" semantics.

[ronnygunawan]

@alrz x is y syntax no longer possible because RHS must be a constant value. On top of that, we now have records which overrides equality operators by default.

Please reopen dotnet/roslyn#8409?

[alrz]

Feel free to open a discussion here in dotnet/csharplang.

I do believe it still has merits but I guess === brings back memories from JS so the majority dislike it.