Test whether a variable equals either one of two values

Question

I want to test whether a equals 1 or 2

I could do

a == 1 || a == 2

but this requires repeating a (which would be annoying for longer variables)

I'd like to do something like a == (1 || 2), but obviously this won't work

I could do [1, 2].include?(a), which is not bad, but strikes me as a bit harder to read

Just wondering how do to this with idiomatic ruby

Answer 1

Your first method is idiomatic Ruby. Unfortunately Ruby doesn't have an equivalent of Python's a in [1,2], which I think would be nicer. Your [1,2].include? a is the nearest alternative, and I think it's a little backwards from the most natural way.

Of course, if you use this a lot, you could do this:

class Object
  def member_of? container
    container.include? self
  end
end

and then you can do a.member_of? [1, 2].

Answer 2

First put this somewhere:

class Either < Array
  def ==(other)
    self.include? other
  end
end

def either(*these)
  Either[*these]
end

Then, then:

if (either 1, 2) == a
  puts "(i'm just having fun)"
end

Answer 3

I don't know in what context you're using this in, but if it fits into a switch statement you can do:

a = 1
case a
when 1, 2
  puts a
end

Some other benefits is that when uses the case equality === operator, so if you want, you can override that method for different behavior. Another, is that you can also use ranges with it too if that meets your use case:

when 1..5, 7, 10

Answer 4

a.to_s()=~/^(1|2)$/

Answer 5

Maybe I'm being thick here, but it seems to me that:

(1..2) === a

...works.

Answer 6

Another way would be to petition "Matz" to add this functionality to the Ruby specification.

if input == ("quit","exit","close","cancel") then
  #quit the program
end

In fact, the case-when statement lets you do exactly that:

case input when "quit","exit","close","cancel" then 
  #quit the program
end

When written on one line like that, it acts and almost looks like an if statement. Is the bottom example a good temporary substitution for the top example? You be the judge.