Suggestion: Allow ignored lambda parameters to have the name _

[erik-kallen]

When writing lambdas you quite often end up not caring about all parameters, but you need names for them anyway. In F# you can use _ as the name for such parameters, and that is also possible in C# but only as long as there is only one such parameters. If there is more than one you need to come up with names (or use names such as _1, _2 etc).

My suggestion is to allow multiple symbols in the same scope be named _. Of couse, when doing this you can't use any of the symbols with that name, but it will enable you to write things like MyMethod((a, _, _) => a + 1) which is sometimes convenient (especially when using mocking libraries).

[AdamSpeight2008]

Doesn't work for vb.net _ is the line continuation character,

[xbelt]

Well it does not necessarly need to be the underscore. I could also imagine somethind like:
(a, ?,?) => a + 1
or simply
(a, ,) => a + 1
Personally I find this a nice idea

[HaloFour]

Check out #20 and #2145.

Since the pattern matching spec is very likely to include a wildcard, which thus far as been *, I'd recommend reusing that character in these cases.

Note that _ is a legal identifier today. Changing the meaning would break code. The C# team is a lot less willing to do this than the Java team (where this very transition is already underway).

[AdamSpeight2008]

@xbelt I also like the look of the second option (a, , ), as I think of that form of syntax as a tuple. It is a tuple<parameter,parameter,parameter>

[erik-kallen]

My suggestion is for C# although it might be useful for vb too but I don't use that language,

Using the underscore for this would not be a breaking change in C# as long as the rule is specified to be that "if more than one symbol in a scope has the name _, an error is not issued but none of those symbols can be accessed". It is not a breaking change because such program is illegal today.

[HaloFour]

Maybe, but it would be silly to have multiple wildcard operators in different contexts. If pattern matching is going to use * then it doesn't make sense for parameter ignoring to use _, especially since _ is a perfectly legal C# identifier.

[aluanhaddad]

@HaloFour Yes, the syntax should definitely align with that of pattern matching.

[gulshan]

This is probably done now with _ discard.

[alrz]

Not just yet. AFAIK it only works on patterns, out var, deconstructors and simple assignments.

[jcouv]

I'll go ahead and close this language proposal in favor of the one in the csharplang repo dotnet/csharplang#111
Thanks