"view objects" for keys(dict) and values(dict)

[daviddelaat]

Currently keys(dict) and values(dict) are Arrays in Julia.

In Python 2 this was also the case, but in Python 3 this was changed to returning "view objects", see: http://docs.python.org/3.0/library/stdtypes.html#dict.keys
I think they got the idea from the Java collections framework.

Personally I like this a lot, what are your opinions about this for Julia?

[pao]

I'm conservatively applying the "breaking" tag, so please remove it if there's no way anyone could be relying on details of the current behavior.

[StefanKarpinski]

No, this seems breaking, therefore 0.2. As long as the view is read-only it seems reasonable, but in that case, you can't do things like sort! the view.

[JeffBezanson]

We could add this easily (yet another use of an immutable type, too), and get arrays of keys with collect(keys(dict)). Seems like a good idea.

[JeffBezanson]

I implemented this and will push it soon. Then contains should be used to see if an element is in a collection, and has only checks for keys in dictionaries, defined as has(d,k) = contains(keys(d),k). Perhaps it should be called haskey.

[kmsquire]

Will (or can you make) contains(d, (k,v)) work?

In working on OrderedDicts (which I will resubmit soon), I have alternated between treating key-value pairs as 2-tuples or their own DictItem type. DictItem seems more performant, but from a user's perspective, being able to treat key-value pairs as tuples is useful.

[daviddelaat]

Thanks Jeff for working on this.

I think haskey is a good idea, the has function name is rather confusing.

[JeffBezanson]

Yes contains(d,(k,v)) should work, and I'm including a change to make it faster for dicts.