Combining abstract types and parametric types?

Let's say I have a type hierarchy like this:

abstract type Parent end
mutable struct Child1 <: Parent
    type # Set to 'child1'
end
mutable struct Child2{N<:Integer} <: Parent
    type # Set to 'child2'
    i::N
end

StructTypes.StructType(::Type{Parent}) = StructTypes.AbstractType()
StructTypes.StructType(::Type{Child1}) = StructTypes.Mutable()
StructTypes.StructType(::Type{<:Child2}) = StructTypes.Mutable()

StructTypes.subtypekey(::Type{Parent}) = :type
StructTypes.subtypes(::Type{Parent}) = (child1=Child1, child2=Child2)

Currently, afaik, there is no mechanism for StructTypes to serialize/deserialize the value of N, like how it can write the type key for each child.

Current workarounds I can think of:

• Pick a unique type name for each concrete version of Child2{N} you expect to be possible: (child1=Child1, child2U8=Child2{UInt8}, child2I32=Child2{Int32}, ...)
• Use UnorderedStruct or OrderedStruct instead of Mutable, and let the type parameter be inferred by the constructor.

Would it be feasible to support deserializing type parameters in the same way as the type itself? For example:

struct Child2{N<:Integer} <: Parent
    type # Set to 'child2'
    int_type::Type # Set to string(N)
    i::N
end
StructTypes.parametrickey(::Type{<:Child2}, ::Val{1}) = :int_type

Start by reviewing the existing StructTypes.StructType, subtypekey, and subtypes entry points described in the issue, then compare them with the proposed parametrickey API. Determine how type-parameter values should be represented and reconstructed, including interaction with abstract subtypes. Done means the behavior and API are specified clearly enough to guide an implementation and its tests.