From: Jacob Fugal <lukfugl@...>
Date: 2009-03-03T13:46:52+09:00
Subject: [ruby-core:22635] Re: Question: lambda and yield

Take the following with a grain of salt; I'm not a core expert, I just
play one on TV. ;) If I'm wrong, just let me know. That said, I'm
pretty sure that...

Try the following code. You'll see that the puts after the yield isn't
even evaluated. The return statement within the lambda is "bound" (for
lack of a better word) to the method where the lambda was defined, not
the lambda itself. The statement is rebound to the Proc object when
the lambda is converted to a Proc, but remains bound to the caller
when yielded to.

Moral of the story: avoid return in lambdas and procs unless you
really want to explode a later code reader's brain. :)

Jacob Fugal

--
def call_block(&l)
  l.call
end

def yield_block
  yield
end

def lambda_and_call
  l = lambda { return 1 }
  x = call_block(&l) + 1
  puts "lambda_and_call: #{x}"
end

def lambda_and_yield
  l = lambda { return 1 }
  x = yield_block(&l) + 1
  puts "lambda_and_yield: #{x}"
end

lambda_and_call
lambda_and_yield