[ruby-core:81437] [Ruby trunk Feature#13606] Enumerator equality and comparison

Issue #13606 has been updated by glebm (Gleb Mazovetskiy).


shevegen (Robert A. Heiler) wrote:

> [...] but they are not entirely the same are they? Different
> object id for most objects for example. But it also may be that I did not fully
> understand the proposal yet.

Most objects in Ruby are compared semantically even if the object IDs are different, including `Array` and `Hash`.

> What would the speed penalty be if one exists?

If the `Enumerator`s have different `object_id`s, previous the equality check was `O(1)` but is `O(n)` with this proposal (just like for `Array`).

> I guess the latter one could be
> handled by some "behavioural switch" for people who need the behaviour
> desscribed in the proposal, so a use-case example would be helpful.


I am not proposing a behavioural switch. This should be a backwards-incompatible change.
Use cases are the same as for arrays, except when the "arrays" are "lazy".

Example:

~~~ ruby
[1, 2, 3].reverse == [3, 2, 1]
#=> true

[1, 2, 3].reverse_each == [3, 2, 1]
#=> false

[1, 2, 3].reverse_each == [1, 2, 3].reverse_each
#=> false
~~~

With this proposal, the last two are also `true`.


----------------------------------------
Feature #13606: Enumerator equality and comparison
https://bugs.ruby-lang.org/issues/13606#change-65141

* Author: glebm (Gleb Mazovetskiy)
* Status: Feedback
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
In Ruby, most objects are compared by value. What do you think about `Enumerator`s following the same pattern? I think this would greatly increase the expressiveness of Ruby.

Proposal:

Two `Enumerator`s should be considered equal (`==`) if they yield the same number of elements and these elements are equal (`==`).
If both of the `Enumerator`s are infinite, the equality operator never terminates.
`<=>` should be handled similarly.



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