[ruby-core:35651] Re: [Ruby 1.9 - Feature #4553] Add Set#pick and Set#pop

The existence of `Set#first` is an artifact of Set including Enumerable and the very idea of "first" on a Set is an odd notion. A set by itself does not have ordering. I have implemented it to pick the first element because it is simplest, but someone calling "pick" on a set does not care which element it is. If one would prefer implementing it as an alias, I'd be fine with that.

On a personal note, one reason I enjoy using Ruby because often my code reads just as I would describe it to a colleague - reading "element = set.first" is not something many would agree is a sensible way to describe the act of picking an arbitrary element from a mathematical set.

And yes, one could implement #pop with #delete and #first, which again relies on a notion of ordering in a set. One can implement #proper_subset with #subset and a comparison, as can one implement #proper_superset with #supserset and a comparison. Yet they are in the Set class because they are fundamental operations. #add? and #delete? can also be implemented with #add and #include?/#delete and #include? respectively, yet they are included in the Set class because they are useful and common operations on a set.

If `pop` is too close the Array method of the same name, I understand the confusion, but I don't get why picking first/last makes a difference. Anyone asking to remove an arbitrary element from a Set surely doesn't care where it lies in an underlying hash table. I am surprised one would argue that the Set class rarely needs the notion of selecting an element from it. Rarely am I presented with an algorithm using sets that does not require simply getting an element or picking one out of a set.

Michael Edgar
[e-mail]
http://carboni.ca/

On Apr 7, 2011, at 2:40 PM, Marc-Andre Lafortune wrote:

> Hi.
> 
> There is no difference between your `Set#pick` and the existing `Set#first`. As such, there is no need for `pick`.
> 
> One can get the effect of `Set#pop` by calling the existing `Set#delete` with the result of `Set#first` (with the same O(1) efficiency).
> 
> I find problematic that a method called `pop` would take the first element; it could be renamed to `shift`, say, or take the last element instead. More importantly, though, I am not convinced that this functionality is that frequently used.