[ruby-core:118902] [Ruby master Feature#20664] Add `before` and `until` options to Enumerator.produce

Issue #20664 has been updated by ufuk (Ufuk Kayserilioglu).


@matheusrich In my opinion `take_until` might be an interesting method to add, but I think we are unnecessarily complicating the example with `it` and `nil?`.

The expression is simply:
```ruby
Enumerator.produce(File, &:superclass).take_while(&:itself)
```
and it works perfectly fine and, IMO, is very readable for anyone who knows enough to reach for `Enumerable.produce` in the first place.

With respect to the original proposal in this ticket, I also find it a little awkward when Ruby methods take something callable other than blocks, but I understand the pragmatic use of the proposed `to_proc`able keyword arguments that would satisfy the majority of cases where one would reach for `Enumerable.produce`.

----------------------------------------
Feature #20664: Add `before` and `until` options to Enumerator.produce
https://bugs.ruby-lang.org/issues/20664#change-109471

* Author: knu (Akinori MUSHA)
* Status: Open
----------------------------------------
Enumerator.produce provides a nice way to generate an infinite sequence but is a bit awkward to define how to end a sequence.  It lacks a simple and easy way to produce typical finite sequences in an intuitive syntax.

This proposal attempts to solve the problem by adding these two options to the method:

- `before`: when provided, it is used as a predicate to determine if an iteration should end before a generated value gets yielded.
- `until`: when provided, it is used as a predicate to determine if an iteration should end until after a generated value gets yielded.

Any value that responds to `to_proc` and returns a `Proc` object is accepted in these options.

A typical use case for the `before` option is traversing a tree structure to iterate over the ancestors or following/preceding siblings of a node.

The `until` option can be used when there is a clear definition of the "last" value to yield.

```ruby
enum = Enumerator.produce(File, before: :nil?, &:superclass)
enum.to_a #=> [File, IO, Object, BasicObject]

enum = Enumerator.produce(3, until: :zero?, &:pred)
enum_to_a #=> [3, 2, 1, 0]
```

---Files--------------------------------
0001-Add-before-and-until-options-to-Enumerator.produce.patch (10.7 KB)


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