[ruby-core:96288] [Ruby master Feature#16428] Add Array#uniq?

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

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

* Author: kyanagi (Kouhei Yanagita)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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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 returns false.
If a block is given, it will use the return value of the block for comparison.

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

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