On Wednesday, November 26, 2014 6:01:56 PM UTC-6, Test This wrote:
I have the following function defined to check whether a record exists in
a Mongodb database (thanks a million for PyCall, which make it easy to use
pymongo
to interact with mongodb in julia).
function
Patrick, thank you for your response and the link. I will need to read it
more carefully and try to understand as it since it deals with concepts I
am not familiar with. However, wouldn't the solution you proposed restrict
all values of the rec Dict to the same type in any given call. Am I
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
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
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
Thanks, now I understand it.
The problem I had was this, which I imagine to exist with many other
non-computer scientists new to Julia.
This topic is discussed under the parametric type section of the manual,
and since I had not attempted to use parametric types (the things with
the
The explanation that made me stop suggesting that `Sometype{T1} :
Sometype{T2} if T1:T2` was the following function:
function foo( a::Array{Any, 1})
# I can now get objects from the array, and they will be subtypes of Any
b = a[1]
# And I can insert Any object into the array
