It is demonstrated in the manual at
http://docs.julialang.org/en/release-0.3/manual/types/#parametric-composite-types
that parametric types do not have any relationship even if their parameter
types have some relationship. Perhaps it would be better emphasise that
and to explain it simply and clearly for the non-*computer* scientists as
something like:
Two parametric types Sometype{T1} and Sometype{T2} have no subtype or
supertype relationship even if T1 has a subtype or supertype relationship
to T2.
Cheers
Lex
On Thursday, November 27, 2014 1:37:53 PM UTC+10, John Myles White wrote:
>
> All types do have Any as a parent.
>
> It is clear that many people are confused about what covariance,
> contravariance and invariance mean in computer science. As such, I very
> strongly encourage everyone who isn't sure that they understand Julia's
> type system to read through the wikipedia article on covariance and
> contravariance:
> http://en.wikipedia.org/wiki/Covariance_and_contravariance_%28computer_science%29
>
>
> Perhaps the Julia manual should have a "prerequisites" section that lists
> all of the concepts that readers are assumed to already understand.
>
> -- John
>
> On Nov 26, 2014, at 7:27 PM, K Leo <[email protected] <javascript:>>
> wrote:
>
> > I ran into similar mental difficulty regarding whether type Any is a
> superset of any other types. I did not find anything to read, but simply
> accepted the fact through painstaking experiments.
> >
> > I think the word "Any" here is confusing. The English definition of it
> means that it ought to include any types. Perhaps we should seek other
> word to define this type. Word like "Mixed" might be more appropriate for
> this?
> >
> > On 2014年11月27日 08:17, Patrick O'Leary wrote:
> >>
> >> You've hit type invariance. In Julia, parametric types are
> invariant--that is, Dict{ASCIIString,Float64} is not a subtype of
> Dict{ASCIIString,Any}.
> >>
> >> For more information on why we use invariant parametric types, search
> the list for "parametric invariant" or similar; there have been a few
> discussions on the topic.
> >>
> >> Patrick
> >
>
>
