[ruby-core:96340] [Ruby master Misc#16436] hash missing #last method, make it not so consistent (it has first)

Issue #16436 has been updated by zverok (Victor Shepelev).


`Hash` doesn't have `#first` either :)

```ruby
Hash.instance_method(:first)
# => #<UnboundMethod: Hash(Enumerable)#first(*)>
#                          ^^^^^^^^^^
```

The `first` method existence is just because of hash being a `Enumerable`, not because "first pair(s) of hash" seen as having some frequently used meaning.

(As a side note, Ruby probably could've had `BidirectionalEnumerable` for collections which can be enumerated both directions without side-effects; this one would be a good place to have `#last` method.)

----------------------------------------
Misc #16436: hash missing #last method, make it not so consistent (it has first)
https://bugs.ruby-lang.org/issues/16436#change-83248

* Author: zw963 (Wei Zheng)
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
``` ruby
(pry):main(0)> h = {x:1, y:2, z:3}
{
    :x => 1,
    :y => 2,
    :z => 3
}
(pry):main(0)> h.first
[
    :x,
    1
]
(pry):main(0)> h.first.first
:x
(pry):main(0)> h.first.last
1
```

last method not exist.

```ruby
(pry):main(0)> h.last

Exception: NoMethodError: undefined method `last' for {:x=>1, :y=>2, :z=>3}:Hash
```

We have to use #to_a to make last working.

```ruby
(pry):main(0)> h.to_a.last
[
    :z,
    3
]

(pry):main(0)> h.to_a.last.first
:z
(pry):main(0)> h.to_a.last.last
3
```






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