[ruby-core:118962] [Ruby master Feature#20664] Add `before` and `until` options to Enumerator.produce

["Eregon (Benoit Daloze) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #20664 has been updated by Eregon (Benoit Daloze).


I think that makes sense, as an opposite of `take_while`:
* `take_while` takes all elements until the block returns falsy, and does not include that element which yielded falsy.
* `take_until` takes all elements until the block returns truthy, and does not include that element which yielded truthy.

If clearly documented that probably solves most of the confusion.
So +1 from me to add `take_until`.

I wonder if there is value in having variants that do include the element that stops, but at least so far in the linked issues there seems to be no such use-case.

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Feature #20664: Add `before` and `until` options to Enumerator.produce
https://bugs.ruby-lang.org/issues/20664#change-109534

* Author: knu (Akinori MUSHA)
* Status: Open
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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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