type stability of map and empty arrays

[mhauru]

I find it desirable that in map(f, T[]), if f is type stable on T, then map would return an empty array of the correct type. At the moment it returns an empty array of type T.

I ran into this when trying to do roughly this:

function f(x::Vector)
    y = map(symbol, x)
    return f(y)
end

function f(x::Vector{Symbol})
    # Do fun.
end

[cstjean]

#7258 It's not a simple issue.

[TotalVerb]

For what it's worth, this problem should be gone in v0.5, to be released soon. The inferred type is used in the empty case.

julia> map(Symbol, [])
0-element Array{Symbol,1}

[mhauru]

That's indeed worth quite a lot.

Also, I found a duplicate: #12513