What is the idiomatic way to yield to the block of the caller's caller?

Question

How should one proceed if one wants to yield to the block of the caller's caller? I came up with the following:

def method1(param)
  method2(param) { |x| yield x if block_given? }
end

def method2(param)
  yield(param) if block_given?   # Can I yield from here
end

method1("String") { |x| puts x } # to here in a more elegant way?

Sergio Tulentsev · Answer 1 · 2013-01-10T15:18:53.787

2

Just pass the block explicitly

def method1(param, &block)
  method2(param, &block)
end

def method2(param)
  yield param if block_given?
end

method1("String") { |x| puts x } # >> String

edited Jan 10 '13 at 15:18

answered Jan 10 '13 at 14:30

Sergio Tulentsev

226,338
43
373
367

Personally I don't dislike the explicit block, but AFAIK orthodoxy says that `method2` should drop the argument `&block` and make a `yield if block_given?` – tokland Jan 10 '13 at 15:16
1

@tokland: agreed. Updated the post. – Sergio Tulentsev Jan 10 '13 at 15:19
@tokland Why is that more orthodox? The answer would be better if it included a motivation for why this particular formulation is good. – N.N. Jan 10 '13 at 18:52
@N.N. I don't have numbers to show, but check code by experienced Ruby coders and you'll see that it's a common practice. The rationale may be like this: 1) `yield` is more idiomatic than `block.call` (that's why the syntantic sugar exists in the first place). 2) If `block` is not used as such it makes no sense to pass it as argument (all Ruby methods can take a block, whether or not there is a block argument). Suprised that https://github.com/bbatsov/ruby-style-guide does not discuss this matter. Check also http://stackoverflow.com/questions/1410160/ruby-proccall-vs-yield – tokland Jan 10 '13 at 19:23

score 2 · Accepted Answer · answered Jan 10 '13 at 14:31

One way is to not use yield in the first method:

def method1(param, &block)
  method2(param, &block)
end

def method2 param
  yield param if block_given?
end

The unary ampersand represents the "block slot" in the method's parameter list. When you pass a block, you can access the block that was passed by putting the & right before the final parameter name. It can be passed around to other methods in the same way.

You can see lots of details about & here: http://ablogaboutcode.com/2012/01/04/the-ampersand-operator-in-ruby/

What is the idiomatic way to yield to the block of the caller's caller?

2 Answers2