Variable inferred as Core.Box due to read-only access after definition

[nalimilan]

With latest git master, in the function below, the type of len is inferred correctly, but not lev is marked as Core.Box. Removing the ntuple call fixes this. In 0.4, the types of both variables are inferred correctly.

Feel free to close if Core.Box isn't actually an indication of type instability (I'm merely trusting @code_warntype here).

function f{N}(x::NTuple{N})
    lev = [length(y) for y in x]
    len = [length(y) for y in x]

    ntuple(i -> length(lev[i]), N)
end

@code_warntype f((1,2))

[yuyichao]

Dup of #15276

[nalimilan]

Ah, I had only looked for Core.Box, but the name wasn't fully qualified a few weeks ago. At least, this issue will help people doing a simple search as I did.

[yuyichao]

To be fair, Box isn't very searchable either.... I can only find it quickly because I pasted it to a more searchable and more recent issue lately....