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uniq! 

        # Array.uniq!

(from ruby core)
---
    array.uniq! -> self or nil
    array.uniq! {|element| ... } -> self or nil

---

Removes duplicate elements from `self`, the first occurrence always
being retained; returns `self` if any elements removed, `nil` otherwise.

With no block given, identifies and removes elements using method `eql?`
to compare.

Returns `self` if any elements removed:
    a = [0, 0, 1, 1, 2, 2]
    a.uniq! # => [0, 1, 2]

Returns `nil` if no elements removed.

With a block given, calls the block for each element; identifies (using
method `eql?`) and removes elements for which the block returns
duplicate values.

Returns `self` if any elements removed:
    a = ['a', 'aa', 'aaa', 'b', 'bb', 'bbb']
    a.uniq! {|element| element.size } # => ['a', 'aa', 'aaa']

Returns `nil` if no elements removed.

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