[ruby-core:109834] [Ruby master Bug#18994] Range#last(n) returns empty for single-element Integer Range

Issue #18994 has been reported by masasakano (Masa Sakano).

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Bug #18994: Range#last(n) returns empty for single-element Integer Range
https://bugs.ruby-lang.org/issues/18994

* Author: masasakano (Masa Sakano)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-darwin20]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
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`Range#last(n)` with a single-element of Integer returns an empty Array. It should return a one-element Array.

Interestingly, when the element is a String, `last(n)` returns a one-element Array, expectedly.

I have checked the behaviour with some selected past versions of Ruby. In up to Ruby-2.6.5, it worked correctly. In Ruby-2.7.0, it doesn't. Nor in Ruby-3, including the current version (Ruby-3.1.2).

The following demonstrates the behaviour (Ruby-3.1.2; same in Ruby-2.7.0). Only the first one does not work in the way it should.

```ruby
(8..8).last(1)        # => []  (!!) (should be: [8])
(8..8).to_a.last(1)   # => [8]
(8..8).first(1)       # => [8]
(?a..?a).last(1)      #=> ["a"]
(?a..?a).to_a.last(1) #=> ["a"]
(?a..?a).first(1)     #=> ["a"]
```




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