Is there an inverse 'member?' method in ruby?

Question

I often find myself checking if some value belongs to some set. As I understand, people normally use Enumerable#member? for this.

end_index = ['.', ','].member?(word[-1]) ? -3 : -2

However, this feels a little less elegant than most of things in Ruby. I'd rather write this code as

end_index = word[-1].is_in?('.', ',') ? -3 : -2

but I fail to find such method. Does it even exist? If not, any ideas as to why?

Answer 1

Not in ruby but in ActiveSupport:

characters = ["Konata", "Kagami", "Tsukasa"]
"Konata".in?(characters) # => true

Answer 2

You can easily define it along this line:

class Object
  def is_in? set
    set.include? self
  end
end

and then use as

8.is_in? [0, 9, 15]   # false
8.is_in? [0, 8, 15]   # true

or define

class Object
  def is_in? *set
    set.include? self
  end
end

and use as

8.is_in?(0, 9, 15)   # false
8.is_in?(0, 8, 15)   # true