Update list-patterns.md

[alrz]

No description provided.

[alrz]

📝 This definition was removed in a previous PR.

[333fred]

Why do we need to add it back? Both concepts already exist via the C# features around range and index, I'm not sure we should duplicate here.

[alrz]

Reverted.

[alrz]

A couple of questions:

• Should iTuple switch { (1,2,3) => 1, [1,2,3] => 2, _ => 0 } produce an error? ITuple is both countable and indexable.
• In [..[1], 2] we only check length on the outer list (length=2) but we still check indexer values off of slice (if not subsumed by another test anywhere else). Is that ok?

[333fred]

Should iTuple switch { (1,2,3) => 1, [1,2,3] => 2, _ => 0 } produce an error? ITuple is both countable and indexable.

I don't see how it could, unless we wanted to make assumptions about general correspondence between positional pattern indexes and list pattern indexes. This doesn't seem like a necessarily-safe assumption to me.

In [..[1], 2] we only check length on the outer list (length=2) but we still check indexer values off of slice (if not subsumed by another test anywhere else). Is that ok?

Seems both find and desirable to me. That's what the pattern says should happen, so we should do it.

[333fred]

Why do we need to add it back? Both concepts already exist via the C# features around range and index, I'm not sure we should duplicate here.

[alrz]

Should iTuple switch { (1,2,3) => 1, [1,2,3] => 2, _ => 0 } produce an error? ITuple is both countable and indexable.

I don't see how it could

Because ITuple can be matched with both a list pattern and a positional pattern, the codegen would be identical.

In fact, anything we specified for pattern compatibility here applies to ITuple, including the positive values for length.

[jcouv]

Should iTuple switch { (1,2,3) => 1, [1,2,3] => 2, _ => 0 } produce an error? ITuple is both countable and indexable.

I'm unsure about this one. Let's assume this shouldn't produce an error for now, treating the positional and the list patterns as orthogonal.
We can bring up to LDM when back in session (in 3 weeks).

In [..[1], 2] we only check length on the outer list (length=2) but we still check indexer values off of slice (if not subsumed by another test anywhere else). Is that ok?

Yes, that sounds good to me as well. This behaves the same as when the nested list-pattern has a designation.

[333fred]

Only thing I'm missing from signing off is the answer to why we're adding back the definition of indexable and countable here. I don't think they need to be in this document.

[alrz]

I'm unsure about this one. Let's assume this shouldn't produce an error for now, treating the positional and the list patterns as orthogonal.

This is like mixing {Length:N} and list patterns. The result is the same across all pattern forms.

[jcouv]

FYI, added a note to test plan to follow up on ITuple question.