Ruby中.in?方法的含义是什么？求相关官方文档

The .in? method checks if the object it's called on exists within the collection passed as its argument.

In your code line if !'Region'.in? region, it's verifying whether the string 'Region' is not present in the region collection (the ! is a negation operator).

Key details: #

• This method is not part of core Ruby—it's added by Active Support, a utility library included with Ruby on Rails.
• It's essentially a reverse of the core Ruby include? method. So 'Region'.in?(region) is equivalent to region.include?('Region')—the difference is just readability (some prefer the "element in collection" phrasing over "collection includes element").

Example usage: #

# If region is an array like ['Region', 'Country', 'City']
'Region'.in? region # => true
'Planet'.in? region # => false

# Negated version (like your code)
! 'Region'.in? region # => false (since 'Region' is present)

Documentation note: #

Since .in? comes from Active Support, you can find its official documentation in the Ruby on Rails Active Support API reference, under the Object class methods.

内容的提问来源于stack exchange，提问作者Al Pa chino