Object#returning (Ruby's K Combinator)

http://weblog.jamisbuck.org/2006/10/27/mining-activesupport-object-returning

by raganwald • 18 years ago

10 15 18 years ago

weblog.jamisbuck.org

pius• 18 years ago

It's (perhaps) worth noting that Object#returning is part of ActiveSupport, not the Ruby Standard Library.

raganwald6• 18 years ago

True, and worth noting. Also of interest: Ruby 1.9 includes a different implementation of the K Combinator, Object#tap. It's a method rather than a pseudo-function, so instead of:

  returning (Fubar.new) do |f|
    ...
  end

Your write:

  Fubar.new.tap do |f|
    ...
  end

Shameless plug-whoring: The andand gem includes an enhanced Object#tap: http://andand.rubyforge.org

ionfish• 18 years ago

I had a couple of spare minutes so I did a JavaScript implementation.

http://gist.github.com/7727

Harkins• 18 years ago

Also see http://kcombinator.com

eru• 18 years ago

Side-effects are evil!

raganwald6• 18 years ago

Here's a use for the K Combinator that isn't Your Father's Imperative Programming. I sometimes want an arbitrary, one-off object when testing or prototyping things, perhaps in irb:

  foo = returning(Object.new) do |f|
    def f.bar
      ...
    end
    def f.bash
      ...
    end
  end

zenspider3• 18 years ago

  foo = returning(Object.new) do |f|
    def f.bar
      ...
    end
    def f.bash
      ...
    end
  end

  # vs

  foo = Object.new
  def foo.bar
    ...
  end
  def foo.bash
    ...
  end

1 line shorter, less indentation, more clear. What does returning get you besides another message send and block activation? I have yet to see a good use for it. (yes, I'm biased. calibrate accordingly)

rob_rasmussen• 18 years ago

For a different perspective on Object#returning, (and Symbol#to_proc and friends), see http://wiki.merbivore.com/pages/it-is-a-bug-if

merb is one of the best-written Ruby libraries I've seen, in large part because they're focused on avoiding clever code.

raganwald6• 18 years ago

I agree that it is a bug to use Symbol#to_proc or Object#returning in merb, however I suggest that neither of these things are "clever."

Instead, I note that neither of these things are part of the standard library today. Which means, you must open the Object or Symbol classes to implement them. Nothing wrong with that in your code, but when you do so in a framework like merb (or Rails!), everyone using your framework gets your little patches in their namespace as well.

My feeling is that with the way Ruby's global class namespace works today, opening a core class has much more serious consequences when you are writing a framework, gem, or plug-in then when you are writing code that does not have "downstream clients."

stcredzero• 18 years ago

Yup. Everything shoved into the dictionary named Smalltalk, including "isA" methods for every subsystem you've written shoved up to Object isn't a big deal for in-house development. When you publish a library or grab one from somewhere, then it becomes a big problem. Then you want namespaces.

So the real-world experience for Smalltalk is that the former is mostly FUD. The latter is a real issue. I suspect that this pretty much applies to the other dynamic languages as well.

zenspider3• 18 years ago

Well, that's partially false. #to_proc is in 1.9.

I also completely and totally disagree that they're not clever. There is nothing _not_ clever about #returning. It is second only to using inject because you're too lazy to assign to a variable first. Nevermind that every railz0r that does that ignores the fact that they've now assigned N times instead of once.

Clever code, in my mind, is a form of hidden cost. It seems to be what I get paid to deal with (read: remove) the most.

Object#returning (Ruby's K Combinator)

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