Struct Parametric struct with type constrains in Union

General Usage
3

Thanks for the fast answer!
The drawback seems to be that the resulting type changes, if I understand it correctly depending on what concrete type I use in each thing.

Is the following solution I found better?
(Taken from different topic )

struct thin{T}
    p::Union{Float64,T}
    someother_member
    function thin{T}(p,someother_member) where {T}
        T <: Function || throw(ArgumentError("invalid type"))
        new{T}(p,someother_member)
    end  
end

I can call every type of p via thing{Function}(p0,some0) and it has the type

thing{function}

I just don’t know whether that is a performance advantage.