Is accessing the `instance` field of a singleton type supported usage?

General Usage
1

The above technique is very useful in rare cases, but I wonder whether it’s supported? I don’t think it’s documented.

For example; is the below guaranteed to work with future Julia versions?

julia> Tuple{Nothing, Nothing, Missing, Val{Val(2)}}.instance
(nothing, nothing, missing, Val{Val{2}()}())

FTR (for people other than Mason), an alternative technique, based on documented inner constructor behavior, for accomplishing the same task is demonstrated here:

2

It’s probably worth noting that, although potentially useful, these techniques may also be dangerous, because they bypass inner constructors. Example:

julia> struct InstancesDisallowed
         InstancesDisallowed() = error("no can do")
       end

julia> InstancesDisallowed.instance
InstancesDisallowed()

julia> InstancesDisallowed()
ERROR: no can do

I think that a type’s inner constructor being bypassable is something that could hypothetically turn out to be unpleasantly surprising for someone in some situation.

3

if you’re asking if this is part of public API that follows semVer, no.

Is it likely to change? also no.

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