Extending Base.in type-stably

General Usage
12

So I tried to remove return type instability of all in methods of Base module, but the problem still persists.

Specifically, I tracked down all the in methods returning Any in the Base module, and annotated their return types wth ::Bool. Then I could see that Base.in always returns either Union{} or Bool:

julia> VERSION
v"0.7.0-DEV.1283"

julia> Base.return_types(Base.in)
28-element Array{Any,1}:
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Union{}
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Bool
 Union{}
 Bool
 Bool
 Bool
 Bool

Then, I repeated the original experiment with MyAbs and MyTypes, hoping that now type stability of the extended Base.in would be recovered. Unfortunately it didn’t:

julia> @code_warntype zero_in(mvec)
Variables:
  #self#::#zero_in
  mvec::Array{MyAbs,1}
  t::Any
  #temp#::Int64
  m::MyAbs

Body:
  begin
      t::Any = false
      #= line 4 =#
      #temp#::Int64 = 1
      4:
      unless (Base.not_int)((#temp#::Int64 === (Base.add_int)((Base.arraylen)(mvec::Array{MyAbs,1})::Int64, 1)::Int64)::Bool)::Bool goto 17
      SSAValue(2) = $(Expr(:invoke, MethodInstance for getindex(::Array{MyAbs,1}, ::Int64), :(Base.getindex), :(mvec), :(#temp#)))::MyAbs
      SSAValue(3) = (Base.add_int)(#temp#::Int64, 1)::Int64
      m::MyAbs = SSAValue(2)
      #temp#::Int64 = SSAValue(3)
      #= line 5 =#
      t::Any = (0 in m::MyAbs)::Any
      #= line 6 =#
      unless t::Any goto 15
      goto 17
      15:
      goto 4
      17:
      #= line 8 =#
      return t::Any
  end::Any

So I guess our analysis was wrong. There is something else causing this instability.

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