RFC: Some Ideas to Tackle #15276 - performance of captured variables in closures

[Mason]

@uniment

P.S. I decided to explore how closures function in the presence of @goto. While exploring that, I contrived some degenerate code which seems to expose an obscure bug in the boxing logic.

@uniment

One might argue that this isn’t actually a bug, but such an argument becomes strained when you try changing baz’s last line to return f, i, in which case f.i is a Core.Box(3.0).

nbd, but interesting.

It’s definitely a bug, and it doesn’t require @goto.

julia> function baz2()
           j = 0
           local f, i
           while j < 3
               i = j + 1
               println("i is now ", i)
               if !(j > 0)
                   f = () -> i
               end
               j += 1.0
           end
           f, nothing
       end;

julia> baz2()[1]()
i is now 1
i is now 2.0
i is now 3.0
1

julia> function baz3()
           j = 0
           local f, i
           while j < 3
               i = j + 1
               println("i is now ", i)
               if !(j > 0)
                   f = () -> i
               end
               j += 1.0
           end
           f, i
       end;

julia> baz3()[1]()
i is now 1
i is now 2.0
i is now 3.0
3.0

Would you mind filing a bug report?