Proposal to add methods to homogeneous tuples (`(T, T, ..., T)`) so that they can be used as slices (`&[T]`)

[nikomatsakis]

Title says it all!

[nikomatsakis]

Implemented in rust-lang/rust#14604

[Valloric]

IMO the RFC as presented is fine, but this alternative really is more elegant. I'd prefer it if at all possible.

[glaebhoerl]

For what it's worth this would be subsumed by #91 (Coercible). The awkwardness of things like making fixed-length arrays be the supertypes of homogenous tuples, or vice-versa (both directions are valuable), was one of the things which pushed me away from the subtyping model in the first place.

W.r.t. indexing tuples, I've had the idea that their components could be exposed as fields, except numbered rather than named, so: my_tup.2 is the third component of the tuple (if there is one, otherwise compile error), (3, 1, 4, 5, 9).3 == 5, etc. Same for tuple structs. This would close a noticeable features gap relative to structural structs. It could be extended to fixed-length arrays as well.

[bstrie]

Given that this would only work on homogenous tuples I suppose that this wouldn't preclude the possibility of allowing the compiler to optimize tuple representation?

[bstrie]

@glaebhoerl, given that these methods would only be implemented on tuples that are congruent to arrays, I think we might as well just reuse the existing array indexing syntax.

[glaebhoerl]

@bstrie The methods @nikomatsakis is proposing would only be for homogenous tuples... but the .0 .1 .2 etc. fields I was floating are for all tuples. (Again, the analogy is struct fields.) Anyway, these ideas are all complementary, I just wanted to mention it because it's related (but otherwise it should have its own RFC).

[eddyb]

This is one of the tricks I realized I could have in the library, using VG. I think the old-style RFC has an example of it, actually.
This enables Vec::new(a, b, c, ...) or HashMap::new((k0, v0), (k1, v1), ...), among other useful patterns.

[nikomatsakis]

We decided in meeting to take no action here (yet).