Subtype ArrayPartition and NamedArrayPartition

We want to use a NamedArrayPartition as our u0 in a problem to replace a DEDataArray which we used (for not much good reason) and NamedArrayPartitions have the functionality we really want. However we need to be able to multiple dispatch on the 'type' of u0 we build (aka the fields we have assigned) and therefore want to use NamedArrayPartition as a supertype to subtype from. Something like the below:

mutable struct test_struct <: NamedArrayPartition
    x :: Vector{Real}
    y :: Matrix{Real}
    z :: AnyothersupportedtypebyNamedArrayPartition
end 

Start by reading the implementation and type definition of NamedArrayPartition, then check Julia's subtype and multiple-dispatch constraints for the proposed mutable struct. Done means a user-defined struct can subtype NamedArrayPartition while retaining the supported partition contents and can be dispatched on by its concrete type.