"forwarding" of properties

General Usage
1

I am very excited about getproperty & friends in 1.0, as it would make a particular package I am working on have a much simpler API. I could not find a lot of guidance about it though at the moment, so I am learning from the examples (eg in LinearAlgebra).

I am wondering about the possibility of “forwarding” all properties which are not fields to a particular field. MWE:

import Base: propertynames, getproperty

"Subtypes have a field `x`, used for properties not in `fieldnames`."
abstract type ForwardOnX end

propertynames(w::ForwardOnX) = (fieldnames(w)..., propertynames(w.x)...)

function getproperty(w::TX, name::Symbol) where {TX <: ForwardOnX}
    if name ∈ fieldnames(TX)
        getfield(w, name)
    else
        getproperty(w.x, name)
    end
end

struct Test0{A}
    a::A
end

struct Test1{X,B} <: ForwardOnX
    x::X
    b::B
end

t0 = Test0(:a)
t1 = Test1(t0, :b)
t0.a # :a
t1.a # :a
t1.b # :b, the relevant field
t1.x # the relevant field

Is this an OK pattern? I am hoping it would compile to reasonably efficient code with constant folding. Anything I could do to improve it?

2

PS: probably

propertynames(w::ForwardOnX) = unique((fieldnames(w)..., propertynames(w.x)...))

would be nicer.