Inconsistent restriction when subtyping using typealias #19414
Closed
Description
julia> abstract Foo{T}
julia> typealias Bar{T} Foo{T}
Foo{T}
julia> typealias Baz Foo
Foo{T}
julia> type A <: Foo; end
julia> type B <: Bar; end
ERROR: invalid subtyping in definition of B
julia> type C <: Baz; endArguably, having a supertype with unfixed parameters is not very useful (or am I missing something?), but if it works for A and C, why shouldn't it for B?
Somewhat more concrete:
julia> type UntypedVector <: AbstractVector; end
ERROR: invalid subtyping in definition of UntypedVector
julia> type UntypedVector <: AbstractArray{TypeVar(:T),1}; end # then try this instead
julia> supertype(UntypedVector) == AbstractVector
trueThe root cause seems to be that in the cases that work, the given supertype is a DataType, while in those that don't, it is a TypeConstructor. Might make sense the way it is, but for a casual observer, above examples just look really inconsistent.