NaI returned for valid interval

[lucaferranti]

julia> interval(typemin(Int64), typemax(Int64))
┌ Warning: ill-formed interval [a, b] with a = -9223372036854775808, b = 9223372036854775807 and decoration d = com. NaI is returned
└ @ IntervalArithmetic ~/.julia/packages/IntervalArithmetic/7EbAT/src/intervals/construction.jl:413
∅_ill

despite that should be a valid interval. I think this happens because of the definition

is_valid_interval(::Flavor{:set_based}, a::Real, b::Real) = b - a ≥ 0

and b - a overflows in this case

julia> typemax(Int64) - typemin(Int64)
-1

I guess the motivation for not writing the check as b >= a was disallowing interval(Inf, Inf), or was there another compelling reason?

[lucaferranti]

haven't tested, but the following might work

function is_valid_interval(::Flavor{:set_based}, a::Real, b::Real)
  a == b && return !isinf(a)
  return b ≥ a
end

[OlivierHnt]

Good catch!

I guess the motivation for not writing the check as b >= a was disallowing interval(Inf, Inf), or was there another compelling reason?

I think so. Maybe this is better to prevent branching

is_valid_interval(::Flavor{:set_based}, a::Real, b::Real) = ifelse(a == b, !isinf(a), b > a)

Do you want to make the PR?