Question

Why does this method return 1 rather than dying from infinite recursion?

def foo
  foo ||= 1
end

foo # => 1

Rewritten the following way it does die:

def foo
  foo.nil? ? 1 : foo
end

Answer 1

In the first case, foo ||= 1 refers to a local variable. Ruby always creates a local variable when you do assignment on a bareword, which is why you have to write self.foo = ... if you want to invoke a writer method defined as def foo=(value). The ||= operator is, after all, just a fancy assignment operator.

In the second case, there is no assignment, so when it hits foo.nil?, Ruby interprets the bareword foo as a method call, and blows up.