convert with same type does not use the correct method

[schillic]

I noticed a recent problem when converting intervals.
The relevant definitions are here:

IntervalArithmetic.jl/src/intervals/conversion.jl

Lines 19 to 20 in 1516c5e

	convert(::Type{Interval{T}}, x::Interval{T}) where {T} = x
	convert(::Type{Interval{T}}, x::Interval) where {T} = atomic(Interval{T}, x)

To me they look correct, and I think until recently they worked as expected. In particular, the first method should fire if source and target type are identical. Below are the results in a fresh environment with Julia v1.2.0-rc2:

(v1.2) pkg> st
    Status `~/.julia/environments/v1.2/Project.toml`
  [d1acc4aa] IntervalArithmetic v0.16.0

julia> using IntervalArithmetic

julia> N = Float64; i = N(0) ± N(1)
[-1, 1]

julia> convert(typeof(i), i)
[-1, 1]

julia> @which convert(typeof(i), i)
convert(::Type{Interval{T}}, x::Interval) where T in IntervalArithmetic at .julia/packages/IntervalArithmetic/4e8KJ/src/intervals/conversion.jl:20

So the wrong method is used (the more general one). With Rationals this even crashes.

julia> N = Rational{Int}; i = N(0) ± N(1)
[-1//1, 1//1]

julia> convert(typeof(i), i)
ERROR: MethodError: no method matching atomic(::Type{Interval{Rational{Int64}}}, ::Interval{Rational{Int64}})

I realized this in a recent rebase of a pull request in Julia v1.0 and v1.1. The build was green before, and since this was after your latest release, the problem is probably not on your side. But I am out of ideas.
Note that this works:

julia> @which convert(Rational{Int}, 1//1)
convert(::Type{T}, x::T) where T<:Number in Base at number.jl:6

[lbenet]

I reproduce both problems on Julia 1.1.1. The second problem is understandable (lack of a method)...

[schillic]

The second problem is understandable (lack of a method)...

True, but it only goes there because it does not pick the correct method in line 19...

[dpsanders]

This is a weird bug. I don't know why it's happening, but I have a fix in #320.

This should probably be reported as a Julia bug.

[schillic]

Thanks a lot!
Since it happened all of a sudden, I suspect that some of your dependencies committed type piracy. I did not update my Julia version.

[dpsanders]

Reported on JuliaLang here:
JuliaLang/julia#32884

[dpsanders]

This happens with no other packages loaded, so I don't think any dependencies are involved?

[schillic]

Right, it's just a mystery.

[dpsanders]

Jeff answered in the above issue.

Did this actually cause any problems for you?

[schillic]

Yes, because of the Rationals. And it's also less efficient of course.

EDIT: Here is a simple example to show my problem:

julia> using IntervalArithmetic

julia> i = Interval(0//1 ± 1//1)
[-1//1, 1//1]

julia> [i, i]
ERROR: MethodError: no method matching atomic(::Type{Interval{Rational{Int64}}}, ::Interval{Rational{Int64}})
Closest candidates are:
  atomic(::Type{Interval{T<:AbstractFloat}}, ::Interval) where T<:AbstractFloat at /.julia/packages/IntervalArithmetic/1T5or/src/intervals/conversion.jl:123
  atomic(::Type{Interval{T<:AbstractFloat}}, ::S<:Real) where {T<:AbstractFloat, S<:Real} at /.julia/packages/IntervalArithmetic/1T5or/src/intervals/conversion.jl:96
  atomic(::Type{Interval{Rational{Int64}}}, ::Irrational) at /.julia/packages/IntervalArithmetic/1T5or/src/intervals/conversion.jl:133
  ...
Stacktrace:
 [1] convert(::Type{Interval{Rational{Int64}}}, ::Interval{Rational{Int64}}) at /.julia/packages/IntervalArithmetic/1T5or/src/intervals/conversion.jl:20
 [2] setindex!(::Array{Interval{Rational{Int64}},1}, ::Interval{Rational{Int64}}, ::Int64) at ./array.jl:767
 [3] vect(::Interval{Rational{Int64}}, ::Vararg{Interval{Rational{Int64}},N} where N) at ./array.jl:130
 [4] top-level scope at none:0

I still do not understand why this was no problem before, but the fix seems to be easy to do now.

[lbenet]

So, should we restrict the types always?

[dpsanders]

Maybe we should restrict the types, but that's a lot of code to work through...

[dpsanders]

The Rational case works now after #320 . Thanks for the report!