Oh how very silly of me. As soon as I pressed enter I figured out the right
way to do this.
abstract Ring
abstract EuclideanDomain <: Ring
abstract Field <: EuclideanDomain
type Poly{T <: Ring} <: Ring
end
type ZZ <: EuclideanDomain
end
type QQ <: Field
end
PolynomialRing{T <: Ring}(::Type{T}) = Poly{T}
function PolynomialRing{T <: Field}(::Type{T})
R = Poly{T}
R.super = EuclideanDomain
return R
end
So with those definitions, here is the result:
julia> R = PolynomialRing(ZZ)
Poly{ZZ} (constructor with 1 method)
julia> R <: EuclideanDomain
false
julia> S = PolynomialRing(QQ)
Poly{QQ} (constructor with 1 method)
julia> S <: EuclideanDomain
true
julia> ZZ <: EuclideanDomain
true
julia> QQ <: EuclideanDomain
true
julia> type Robert <: EuclideanDomain
end
julia> Robert <: EuclideanDomain
true
This is so elegant I can actually use it in Nemo. Great!
Bill.
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