Pattern DUCase _ matches DUCase

[TysonMN]

The following code compiles, but it expected that it would not compile.

type MyDU = DUCase
let asdf = function
  | DUCase _ -> ()

I thought the last line would have to omit the discard pattern, which would look like | DUCase -> ().

This behavior is the opposite of bug #9520.

I am using

• version 16.7.5 of Visual Studio Enterprise 2019 and
• version 3.1.402 (x64) of the .NET Core SDK.

[cartermp]

This appears to have been the case for at least F# 4.5, so I don't think it's a bug

[TysonMN]

Is this possibility mentioned in the Wildcard Pattern section of the Pattern Matching documentation? I don't get the impression that it is mentioned there.

[abelbraaksma]

@cartermp is quite right (at least since F# 4.0). I raised this back in 2016, @dsyme considered it kinda by design but was open to changing this behavior (I doubt it's worth its while). See #1592

[cartermp]

Thanks for the clarification @abelbraaksma - I will close as a duplicate of #10204

[abelbraaksma]

I think you meant duplicate of #1592 ;).

[cartermp]

Indeed! The 'ole copy paste 'a 'roo

[TysonMN]

Thanks everyone for all the comments and the pointer to the previous issue. I created dotnet/docs#20858 to suggest that the documentation be changed to mention this feature.

[abelbraaksma]

May be fixed by: #14055

[abelbraaksma]

Yep, fixed indeed! In #14055.