Ruby accessing outer variables in nested function

Question

I'm sure there's a simple answer for this; I just can't seem to find it. I made a nested function in Ruby, and I was having trouble accessing variables from the outer function inside the inner function:

def foo(x)
  def bar
    puts x
  end
  bar
  42
end

foo(5)

I get: NameError: undefined local variable or methodx' for main:Object`

The analogous Python code works:

def foo(x):
  def bar():
    print x
  bar()
  return 42

foo(5)

So how do I do the same thing in Ruby?

An important (but subtle) distinction here is that def...end defines a method, not a function. use lambda/proc to define functions and capture local variables in a closure, as tadman shows. — rampion
– rampion, Commented Jun 19, 2009 at 5:30

tadman · Accepted Answer · 2009-06-19 05:07:12Z

56

As far as I know, defining a named function within a function does not give you access to any local variables.

What you can do instead is use a Proc:

def foo(x)
  bar = lambda do
    puts x
  end
  bar.call
  42
end

foo(5)

answered Jun 19, 2009 at 5:07

tadman

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