Add list patterns proposal

[alrz]

Tracking issue: #3435
Discussion: #1510, #1039, #898
Prototype: dotnet/roslyn@main...alrz:list-patterns
Proposal: Rendered

[gafter]

Really nice work!

List initializers (e.g. in an object creation expression) look like { 1, 2, 3 }, so by A design principle for Programming With Data in #3107 the pattern form "should" use curly braces instead of square brackets. Do you see issues with that? I don't think there is a clash because a property pattern contains PropertyName: before each pattern.

[alrz]

the pattern form "should" use curly braces instead of square brackets. Do you see issues with that?

Unfortunately, with braces, empty list pattern would be ambigious with property pattern clause.

[YairHalberstadt]

IEnumerable support can def be added

I would suggest allowing pattern based enumeration as well, same as foreach.

[alrz]

Updated based on the latest LDM decisions. @333fred @jcouv please review.

[jcouv]

Done with review pass (iteration 11)

[jcouv]

LGTM Thanks (iteration 12) with minor follow-up comments.

[jcouv]

Tagging @333fred for a second look. Thanks

[333fred]

A couple of clarity comments.

[jcouv]

Cool. Thanks for writing this up and sorting many questions. We'll start looking at your roslyn-side change now :-)