Failure of Interval{T}(x::AbstractIrrational)

[mfherbst]

The exported function Interval{T}(x::AbstractIrrational) currently fails:

julia> Interval(π)
ERROR: MethodError: no method matching atomic(::Type{Interval{Float64}}, ::Irrational{:π})

Closest candidates are:
  atomic(::Type{T}, ::Any) where T<:Union{AbstractFloat, Rational}
   @ IntervalArithmetic ~/.julia/packages/IntervalArithmetic/fEeQI/src/intervals/construction.jl:250

Stacktrace:
 [1] #s30#144
   @ ~/.julia/packages/IntervalArithmetic/fEeQI/src/IntervalArithmetic.jl:124 [inlined]
 [2] var"#s30#144"(T::Any, ::Any, x::Any)
   @ IntervalArithmetic ./none:0
 [3] (::Core.GeneratedFunctionStub)(::Any, ::Vararg{Any})
   @ Core ./boot.jl:602
 [4] Interval(x::Irrational{:π})
   @ IntervalArithmetic ~/.julia/packages/IntervalArithmetic/fEeQI/src/IntervalArithmetic.jl:129
 [5] top-level scope
   @ REPL[2]:1

[mfherbst]

I should maybe add that interval(π) works, but I suppose it makes sense to have this one around as well.

[OlivierHnt]

Thanks for reporting the issue. I presume you are using IntervalArithmetic.jl v0.21.1?

[mfherbst]

yep, indeed.

[OlivierHnt]

Ah I see the issue, some lines of code were not properly removed when we released 0.21.

Let me say that Interval as a constructor was purposely removed since it was too close semantically to interval. However the latter is compliant with the standard, while the former is not. In the end we just removed everything for consistency (even though Interval(::AbstractIrrational) should also be a safe constructor).
If you need to recover the "unsafe construction" (I do not advise it) there is an unexported unsafe_interval function.

So the "bug" here is that the error message is not the right one.

[mfherbst]

(even though Interval(::AbstractIrrational) should also be a safe constructor).

I see, thanks for your quick response.

I understand the overall decision of the redesign of IntervalArithmetic, but let me just add my two cents: My use case of intervals is also a little more on the pragmatic side, such as #580. For me conversions like Interval(::AbstractIrrational) get called in my code during "normal operation" during Julia's normal type promotion / conversion. Given that this is a safe constructor, would it not make sense to keep it for convenience ?

[OlivierHnt]

Yes indeed. After discussions, we truly wanted an Interval object that could not be "accidentally" produced from generic code. This means fighting against Julia's (amazing) flexibility at the cost of interoperability and inconvenience.
In particular, we wanted to have users spelling out the constructor function, here interval, and not rely on a "type constructor"; e.g.

generic_function(::Type{T}, a) where {T} = T(log(a))
generic_function(Interval, 3) # danger zone

That being said, issue #580 (see also #568, #584) is being worked on currently (I should have a PR ready very soon 🙂). The idea is that Interval will always be decorated. This will allow us to bring back conversion/promotion and other "mixing" with Number by specifying an appropriate decoration. On the other hand, the current Interval struct will be renamed BareInterval.
Hopefully the next IntervalArithmetic.jl version will feel as convenient as 0.20 did, and at the same time be more reliable.

[mfherbst]

Thanks for your quick response and detailed explanation, much appreciated!