Question

Often, I have a recursive routine within a method that is only called by that method or within the recursive routine itself:

def foo
  ...
  bar
  ...
end

def bar
  ...
  bar
  ...
end

But since bar is not used anywhere else, I do not want to define it as a method but somehow put it inside the method that calls it like this:

def foo
  ...
  bar {# some way to mark the recursive routine
    ...
    bar # some way to call the recursive routine
    ...
  }
  ...
end

Is this possible?

Answer 1

Easy with a lambda/proc:

def foo(n)
  fact = lambda do |i|
    i.zero? ? 1 : i * fact.call(i-1)
  end
  fact.call(n)
end

foo(4) # => 24

You can also use a protected or private method.

If performance is a real concern, creating an object (the lambda) each time will be slower, and calling a lambda is also slower, closure and all. My fruity gem gives me a 3.3x slowdown on this trivial example; the penalty should be much less for cases that actually do something more involved. Just be sure that performance really is an issue; you know what they say about premature optimization…