Issue #8811 has been reported by sawa (Tsuyoshi Sawada).

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Feature #8811: Counterpart to `Hash#key?` for `Array`
https://bugs.ruby-lang.org/issues/8811

Author: sawa (Tsuyoshi Sawada)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


=begin
`Hash` hash `key?` to tell if a key exists without checking the value. It would be convenient if there were a counterpart in `Array`. Suppose it is called `Array#index?`. Then it should behave as follows:

    [1, 2, 3].index?(2) # => true
    [1, 2, 3].index?(3) # => false
    [1, 2, 3].index?(-3) # => true
    [1, 2, 3].index?(-4) # => false

This is useful when we want to insert/move/delete elements to/from a certain position of an array. Without checking if a value exists, it can be messed up. Implementing a check is cumbersome now. With the proposed method, it would become easy.

=end



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