A playful competition: who can define a method that invalidates the most code?

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Yikes, realized I forgot to announce the results on Friday. To evaluate the submissions, I tested each using a script that I executed from the linux prompt to ensure there weren’t differences in my typing at the REPL (since hitting certain keys can force the compilation of new methods). In a couple of cases, this led to a pretty different count than provided by the submitter, perhaps mostly because some REPL methods did not compile. (At least the rank order was consistent with the numbers provided by the applicants.)

Without further ado, here are the results of my analysis and the winners…

For the category of “pirating methods,” we had several submissions including a nail-biter for the win:

  • third place variants of overloading +:
    • the original submission was Base.:+(x::Int, y::Int) = Base.inferencebarrier(Base.add_int(x, y)) (the inferencebarrier isn’t required ) by @simeonschaub at 15782
    • an improved/more evil version Base.:+(x::T, y::T) where {T<:Base.BitInteger} = Base.add_int(x, y) by @StefanKarpinski at 15933
  • second place: Base.getproperty(x, s::Symbol) = getfield(x, s) by @simonbyrne at 17035
  • first place Base.convert(::Type{T}, x::Number) where T<:Real = T(x) by @tomerarnon at 17093

In the non-pirating category, we had:

  • second place struct DoNotCare<:Real end; Base.:(==)(x::DoNotCare, ::Any) = true by @oxinabox at 58
  • convert methods:
    • struct X end; Base.convert(::Any, ::X) = nothing by @oxinabox at 1666 was disqualified (sorry) because to be a valid convert method it should have been Base.convert(::Type{Any}, ::X) (which has 1152 and would have won), so the winner is…
    • first place struct X end; Base.convert(::Union{}, ::X) = nothing by @mbauman at 903

In case you’re curious, in the non-pirating category I believe that it’s not currently possible to do better than the following rather arcane submission:

struct X end
Base._str_sizehint(::X) = nothing

at 2622 invalidations. You can discover this and similar opportunities by installing MethodAnalysis and then running demos/abstract.jl and typing mipriv on the command line. (mipriv means “MethodInstances of private, a.k.a. non-exported, names”; the analog for exported names is miexp).

Congrats to the winners, and let the second phase commence! Announcement will likely be made on Saturday as I am reserving Friday afternoon for a family bike trip.

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