[ruby-core:75039] [Ruby trunk Feature#12080] Enumerable#first, Array#last with block

Issue #12080 has been updated by Shyouhei Urabe.


We looked at this on this month's developer meeting but I remember there was no concrete consensus for this request.

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Feature #12080: Enumerable#first, Array#last with block
https://bugs.ruby-lang.org/issues/12080#change-58164

* Author: Kazuki Yamaguchi
* Status: Open
* Priority: Normal
* Assignee: 
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I propose a new feature: {Enumerable,Array,Range}#first, {Array,Range}#last with block.

If no argument is passed:

* `enum.first { block }` works as the same as `enum.find { block }`
* `ary.last { block }` works as the same as `ary.reverse_each.find { block }`

If a integer is passed:

* `enum.first(n) { block }` works as the same as `enum.lazy.select { block }.first(n)`
* `ary.last(n) { block }` works as the same as `ary.reverse_each.lazy.select { block }.first(n).reverse`

Examples:

~~~ruby
ary = [1, 2, 3, 4, 5, 6]
ary.first    { |i| i.even? } #=> 2
ary.first(2) { |i| i.even? } #=> [2, 4]

ary.last     { |i| i.odd? }  #=> 5
ary.last(2)  { |i| i.odd? }  #=> [3, 5]
~~~

Currently these methods just ignore given blocks.

~~~ruby
ary.first { |i| i > 3 } #=> 1
~~~

---

I sometimes write such code:

~~~ruby
ary = ["DEBUG: a", "WARN: b", ..., "WARN: y", "DEBUG: z"] # assume a large Array
ary.reverse_each.lazy.reject { |line| line.include?("DEBUG") }.first(10).reverse #=> returns last 10 non-debug logs
~~~

But this is redundant and not intuitive. In this case, I just want the last 10 logs which is not debug message in the original order.
With the new Array#last, I can refactor it:

~~~ruby
ary.last(10) { |line| !line.include?("DEBUG") }
~~~

I think this represents what I want to do much more clearly.


---Files--------------------------------
0001-Enumerable-Array-Range-first-Array-Range-last-with-b.patch (11.5 KB)
v2-0001-Enumerable-Array-Range-first-Array-Range-last-wit.patch (14 KB)


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