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 <cnbiz...@gmail.com> 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
>
