For this specific case, why you do not use enumeration? Do you expect users to extend your abstract type?
Perceive that the cost is inescapable, if you used an @Enum or an Int directly to distinguish between the singleton types, then when you wanted to dispatch on these values you would need to wrap them in Val(value). So any code that wants to dispatch on a a field that may store different types (disguised or not) needs to pay the price of type instability. The only ways out I see are:
-
Do not have a single struct with a field that can hold multiple distinct types, have a parametrized struct instead. This is, use
mutable struct MyStruct1{consin <: AbstractType}; x :: Int; end. Dispatch on the type parameter, that will be type stable because it is always the same for the same instance of your parametric type. - Use an implicit or explicit enumeration and then
Valwith the ValSplit package.