Issue #16428 has been updated by kyanagi (Kouhei Yanagita).


I was developing mobile games, and I met these situations:

A card deck can't have duplicate characters.
i.e. `deck.cards.map(&:character_id).uniq.size =3D=3D deck.cards.size`
-> `deck.cards.map(&:character_id).uniq?` or `deck.cards.uniq?(&:character_=
id)`

When players compose items, each of them should be different.
i.e. `materials.map(&:item_id).uniq.size =3D=3D materials.size`
-> `materials.map(&:item_id).uniq?` or `materials.uniq?(&:item_id)`

Another situation:

I developed a registration form for relay runners.
A request body is like this:
```
# Missing sections are allowed. You can send them later.
[
  { section: 1, name: 'aaa' },
  { section: 3, name: 'bbb' },
  { section: 5, name: 'ccc' },
]
```
In this case, duplication of `section` is not allowed.
`runners.map(&:section).uniq.size =3D=3D runners.size`
-> `runners.map(&:section).uniq?` or `runners.uniq?(&:section)`

I think `uniq?` is easier to write and read than `x.uniq.size =3D=3D x.size`
for expression of no duplication. It's even faster.

This check is also found in Ruby's repository (bundler):
https://github.com/ruby/ruby/blob/master/spec/bundler/support/matchers.rb#L=
84

----------------------------------------
Feature #16428: Add Array#uniq?, Enumerable#uniq?
https://bugs.ruby-lang.org/issues/16428#change-85017

* Author: kyanagi (Kouhei Yanagita)
* Status: Feedback
* Priority: Normal
----------------------------------------
I propose Array#uniq?.

I often need to check if an array have duplicate elements.

This method returns true if no duplicates are found in self, otherwise retu=
rns false.
If a block is given, it will use the return value of the block for comparis=
on.

This is equivalent to `array.uniq.size =3D=3D array.size`, but faster.

```
% ~/tmp/r/bin/ruby -rbenchmark/ips -e 'a =3D Array.new(100) { rand(1000) };=
 Benchmark.ips { |x| x.report("uniq") { a.uniq.size =3D=3D a.size }; x.repo=
rt("uniq?") { a.uniq? } }'
Warming up --------------------------------------
                uniq    25.765k i/100ms
               uniq?    76.544k i/100ms
Calculating -------------------------------------
                uniq    278.144k (=B1 4.1%) i/s -      1.391M in   5.010858s
               uniq?    981.868k (=B1 5.1%) i/s -      4.975M in   5.081611s
```

I think the name `uniq?` is natural because Array already has `uniq`.

patch: https://github.com/ruby/ruby/pull/2762



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