Why does `map` of a named tuple and tuple return an array?

Array seems like a strange return type for this interaction:

julia> map(+, (1, 2), (x=1, y=2))
2-element Array{Int64,1}:
 2
 4

Why not tuple?

Because it falls back to the general iterable collection method.

A special method for this could be added, but it may be considered breaking. I think that for mixed arguments, map falling back to collect is fine.

A workaround is

julia> map(+, (1, 2), values((x=1, y=2)))
(2, 4)

I was figuring that was the reason, and changing it now would be breaking. But it just seems like
it should return some kind of tuple - that’s the least surprising option. The workaround is easy, just debugging the issue the first time it happens is weird.

I am not sure — one could argue for a NamedTuple.

I think it is best if map tries to preserve type and structure for homogeneous arguments, and falls back to an Array for heterogeneous ones. This is easy to reason about.

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But array allocates and isn’t type stable

Maybe file an issue so that we track it for Julia 2.0.

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