add a Base.tail method for nonempty tuples

[nsajko]

I have some code that sorts tuples using recursion. When the tuple length gets big (over around 65), suddenly I get lots of allocations in my code, when there should be none. Using @profview_allocs shows that the allocations happen in Base.tail. This simple implementation fixes that.

[nsajko]

If this is good to go, perhaps it would also make sense to reimplement argtail in terms of tail.

[nandoconde]

Not that I am an expert at all, but would not using Any prevent any kind of return type inference here?

[nsajko]

The Any, specifically should have no ill effect. Regarding the question of "does this change affect return type inference?", the answer seems to be "no". The following is the worst case for return type inference, I think, and it's perfect both before and after:

julia> struct S{p}
         v::Int
       end

julia> t = ntuple((i -> S{i}(i)), Val(1000));

julia> using Test

julia> @inferred Base.tail(t);  # no error!

[nsajko]

Indentation fixed (four spaces).

[ViralBShah]

Would be good to get a review and merge.

[jariji]

Perhaps some testing, and a comment or two about why it's written that way?

[CameronBieganek]

Should the tail(x::Tuple) = argtail(x...) method in base/essentials.jl be deleted? Or is it needed for bootstrapping or something like that?

(The empty tuple case is of course handled by the tail(::Tuple{}) method in base/essentials.jl.)

[martinholters]

Seems like something like code_typed(Base.tail, Tuple{Tuple{Int,Int,Int,Vararg{Int}}}) is inferred better with the current implementation than with the proposed one (Tuple{Int,Int,Vararg{Int}} vs. just Tuple).