[ruby-core:119060] [Ruby master Feature#20702] Add `Array#fetch_values`

Issue #20702 has been updated by matz (Yukihiro Matsumoto).


Looks like a good idea. Accepted.

Matz.


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Feature #20702: Add `Array#fetch_values`
https://bugs.ruby-lang.org/issues/20702#change-109638

* Author: toy (Ivan Kuchin)
* Status: Open
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`Array` and `Hash` have matching methods to fetch:

* One value using `[]` (`Array` also allows fetching multiple with range or two arguments)
* One value with default or exception using `fetch` method
* Multiple values using `values_at` method

But only `Hash` has method `fetch_values` to fetch multiple values with fallback or raising an exception (see #10017).

```ruby
hash = {a: 1, b: 2, c: 3}
array = [1, 2, 3]

hash[:b] # => 2
hash[:d] # => nil
array[1] # => 2
array[4] # => nil

hash.fetch(:b) # => 2
hash.fetch(:d) # => IndexError
hash.fetch(:d){ 42 } # => 42
array.fetch(1) # => 2
array.fetch(4) # => IndexError
array.fetch(4){ 42 } # => 42

hash.values_at(:b, :c) # => [2, 3]
hash.values_at(:b, :d) # => [2, nil]
array.values_at(1, 2) # => [2, 3]
array.values_at(1, 4) # => [2, nil]

hash.fetch_values(:b, :c) # => [2, 3]
hash.fetch_values(:b, :d) # => IndexError
hash.fetch_values(:b, :d){ 42 } # => [2, 42]
# missing
array.fetch_values(1, 2) # => [2, 3]
array.fetch_values(1, 4) # => IndexError
array.fetch_values(1, 4){ 42 } # => [2, 42]
```




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