Sams Teach Yourself Ruby in 21 Days

Instance Variables

The variables that we've used so far have local scope. We've likened their use to pronouns in common language: They carry their meaning within some area of communication and then lose that meaning. With only local variables, it would be impossible for an object to remember anything.

forgetful = Object.new
def forgetful.store(v)
  contents = v
end
def forgetful.retrieve
  return contents
end
forgetful.store("left wallet on table")
 forgetful.retrieve   # error: "contents" is undefined!

The variable contents has a scope limited to the method in which it appears, so the value stored by the store method is inaccessible when we try to get it back in the retrieve method; we say that it is out of scope. There is in fact no relationship ...