Irrational numbers are singleton types and are unique, so we have something like
julia> Irrational{:pi}() === Irrational{:pi}()
true
Not many irrational numbers are defined in Base
, therefore packages are free to define their own numbers. However the macro Base.@irrational
that may be used to define a new irrational number a
simultaneously defines Base.Float64(a)
. This therefore means that a second package that also defines the same number a
overwrites the original method definition of Float64(a)
with the new – albeit identical – type. For example:
julia> module A
Base.@irrational a 1.0 float(big(1))
end
Main.A
julia> module B
Base.@irrational a 1.0 float(big(1))
end
Main.B
julia> @which Float64(A.a)
Float64(::Irrational{:a}) in Main.B at irrationals.jl:189
Now this isn’t really a problem for the most part (aside from the unexpected type piracy), since
julia> A.a === B.a
true
and the results would be identical. However when functions are overwritten like this, package precompilation gets broken. One solution appears to be to import A.a
inside B
, but this means that B
needs to depend on A
that might otherwise be unrelated. Another solution is to rename the number in B
and call it something other than a
. However this is undesirable, eg. you wouldn’t name ℯ
as something else. So which package gets to define the number without precompilation hurdles?
For example, StatsFuns.jl defines quite a few irrationals. How to avoid conflicts with StatsFuns
if eg. we want to define sqrt2
?