Get the red out!

[Brian Rogoff]

... of @code_warntype output.

I was reading https://en.wikibooks.org/wiki/Introducing_Julia/Types#Investigating_types and I came across the following code, described as "not very elegant":

level = 0
function showtypetree(subtype)
    global level
    subtypelist = filter(asubtype -> asubtype != Any, subtypes(subtype))
    if length(subtypelist) > 0 
         println("\t" ^ level, subtype)        
         level += 1
         map(showtypetree, subtypelist)
         level -= 1
    else
         println("\t" ^ level, subtype)
    end    
end

showtypetree(Number)

Being unable to leave well enough alone, I decided to try to make it more elegant. After replacing the inelegant global variable with a nested function, I first noticed that the function returns '0', which is ugly. So, the increment operators return a value, which is unfortunate (any reason there's no increment with doesn't do that?) and the two branches of the if return different types. A special 'ignore' function patches that. map also builds and returns a value that's discarded. In OCaml we'd use an 'iter' instead of 'map', but Julia's 'for' can be a one-liner too. I left the print alone even though there's no need to repeatedly build those strings (print_nchars_before is easy)  .In the end I got here

ignore{T<:Any}(value::T)::Void = return

function showtypetree(subtype::DataType)::Void

    level::Int64 = 0

    function nested(st::DataType)::Void

        subtypelist = filter(asubtype -> asubtype != Any, subtypes(st))

        if length(subtypelist) > 0 

            println("\t" ^ level, st)        

            level += 1

            for s in subtypelist nested(s)  end

            ignore(level -= 1)

        else

            println("\t" ^ level, st)

        end    

    end

    nested(subtype)

end

I still notice that when I do @code_warntype showtypetree(Number), I get some 'red', notably, level is shown as Core.Box, even though I explicitly type it. Is there some way to reduce the red in the @code_warntype for this function? Here's what I get in 0.6.0-dev.749

julia> @code_warntype showtypetree(Number)

Variables:

  #self#::#showtypetree

  subtype::Type{Number}

  level::Core.Box

  nested::Core.Box

Body:

  begin

      level::Core.Box = $(Expr(:new, :(Core.Box)))

      nested::Core.Box = $(Expr(:new, :(Core.Box)))

      SSAValue(0) = Main.Void

      (Core.setfield!)(level::Core.Box,:contents,0)::Int64 # line 3:

      SSAValue(1) = $(Expr(:new, :(Main.#nested#2), :(level), :(nested)))

      (Core.setfield!)(nested::Core.Box,:contents,SSAValue(1))::#nested#2 # line 16:

      return (Base.convert)(SSAValue(0),((Core.getfield)(nested::Core.Box,:contents)::Any)(subtype::Type{Number})::Any)::Void

  end::Void

and I'm not sure how to remove the red and make the code more elegant. Ideas?

[Simon Danisch]

How about something like this:

function showtypetree(T, level=0)

    println("\t" ^ level, T)

    for t in subtypes(T)

        (t != Any) && showtypetree(t, level+1)

    end   

end

This is still not type stable, since _subtype seems to use untyped sets:

https://github.com/JuliaLang/julia/blob/master/base/reflection.jl#L283

Not sure if this is an oversight, or if there are actually corner cases making it impossible to type as Set{DataType}().

Fact is, with that change subtype is 10x faster and doesn't return Vector{Any} anymore.

I opened a PR:

https://github.com/JuliaLang/julia/pull/18663

Best,

Simon

[Brian Rogoff]

Thanks Simon, way better, way more Julian. 

-- Brian