Hi --
What no one seems to have (directly) focussed on is that Hash#each
gives two-element [k,v] arrays back as the content.
That's right. And if you wanted things to be "just ducky", it would
have to give only the v. I've actually argued in favor of that before,
b/c it's not unreasonable to see that an Array index is like a Hash
key. So, for a full parallel we'd need to see something like:
{:x=>'m'}.each { |v| v #=> 'm'
['m'].each { |v| v #=> 'm'
{'x'=>'m'}.each_assoc{ |a| a #=> ['x','m']
['m'].each_assoc{ |a| a #=> [0,'m']
One could easily argue that an Assoc class would be quite useful here,
rather than relying on 2-element Array to fulfill the roll. With that
in hand, it would re easy enough to add the #<< method for enumerable
construction.
I don't think there's any reason to expect just the value when
iterating through a hash. In fact if you're using a hash, you
probably have a reason for storing data that way and iterating
pair-wise seems logical to me.
I think it's a question of how one looks at the underlying types or
behaviors. I don't think the language has to converge around the
smallest possible number of interfaces. You can look at it the other
way around. It's useful (extremely) to have hashes, and to iterate
over them in pairs. Enumerable is one way to help introduce that
construct into the language -- not a one-stop-shopping hash
implementation, but helpful.
If we then find fault with hash behavior because it's not in line
precisely with other enumerables, that's a kind of reverse logic; it's
a way to talk the language out of having something useful, which I
don't think is a good idea. Enumerable not only allows but requires
that each class implement #each, and there's no constraint that every
enumerable class has to yield exactly one value at a time. I'd want
to see more concrete evidence that having hashes and arrays behave
differently is really creating problems before wanting to normalize
them around one construct.
I don't necessarily disagree with you. I was following the natural
conclusion of one possible perspective, namely, that the a hash key
corresponds to the array index. It's one possible way to fix the the
issue posited by the thread. And yet, if our hashes were in fact
ordered, as some have asked for, this assumption would fail. So I'm
not actually for it, but it does offer some contrast.
Consider the order hash perspective. We have an index, plus a key and
a value. So in this case, what exactly are we enumerating? We say
"pairs" as if it is something, but Ruby doesn't really have such a
thing. The closest we come to is a 2-element array. Perhaps that is
enough, but it's hardly embraced as such. We see it only in the
iteration of #each _if_ we use a single var. There is no
Hash.new([:a,'x'],[:b,'y']) or hash << [:a,'x'], etc. If there were, I
think this issue wouldn't exist. I think Enumerable would a little
more robust, and we could expect that a Hash be returned from #select.
While the 2-element array covers the need, maybe not so much the want,
and we might even consider a real Pair object:
pair =
a => 'x')
pair.key #=> :a
pair.value #=> 'x'
If we don't take this perspective (irregardless of an actual Pair
class, or not) I don't see any good reason to have Enumerable included
in Hash. Just define the desired "enumerating" methods on Hash itself
--just like #reject. But personally, I'd prefer we get Enumerable
right.
And while were on the subject --it seems that's exactly what we're
doing with String. I hear that String will no longer be Enumerable in
future Ruby. I really just don't get this. What's so problematic with
a default "view" of strings as ordered-sets of characters? All it
requires is the proper definition of #each. Clearly the way things are
now is broken. But does this really require us to scrap String
enumerablity all together? At the very least, how terribly inefficient
it will be to have to convert an string to an array of characters (eg.
bunches of little strings), just to iterate over it.
T.
