It is a bug (in my opinion, but others might disagree), but fixing this
will have consequences for performance in some cases.
Part of problem is that most users want sum to be fast, and that means it
has to be type stable. That means that the type of the sum needs to be
determined only based on the type of the arguments (not their value). This
is often tricky to achieve.
In this case, we can actually know that everything returned by the
ValueIterator is `Int32`, which eltype(values(Dict{Int32,Int32}())) will
reveal. The correct result for sum() will then be zero(Int32) + zero(Int32).
Ivar
kl. 10:48:09 UTC+2 mandag 30. juni 2014 skrev David Gonzales følgende:
>
>
> I came across the following difference:
>
> In[]: sum(collect(values(Dict{Int32,Int32}())))
>
> Out[]: 0
>
> In[]: sum(values(Dict{Int32,Int32}()))
>
> Out[]: ERROR: Argument is empty.
>
> the difference is having an Array vs. an Iterator, but:
>
> In[]: typeof(values(Dict{Int32,Int32}()))
>
> Out[]: ValueIterator{Dict{Int32,Int32}}
>
> So the type of the iterator and hence the zero for the sum initialization
> can be known and a 0 returned (as in the case of an array).
>
> Is this a bug or a feature?
>
>
>
