From: Tom Moertel <tom@...>
Date: 2006-04-20T14:24:50+09:00
Subject: Helper for method pipelines?

Here is a minor coding problem that I suspect is common enough to have
an idiomatic solution.  I just don't know what that solution is.  If
you know of a more Rubyish way, please let me know.

Here's the problem.

Say you have a starting value and want to run it through a method
pipeline to yield a final result.  Part way through the pipeline, you
end up with an intermediate result that you cannot just chain into the
pipeline -- it doesn't have the necessary method.  So you are forced
to save that result into a variable and then pass it into some other
object's method in order to continue the pipeline and yield the final
result:

     intermediate_result =
       value.
       method1(args).
       method2(args)

     final_result =
       some_other_object.method3(intermediate_result)

What I do is add a 'with_self' method to Object that lets me incorporate
foreign method calls into my pipeline:

     final_result =
       value.
       method1(args).
       method2(args).
       with_self { |x| some_other_object.method3(x) }

The definition is straightforward:

     class Object
       def with_self
         block_given? ? yield(self) : self
       end
       def in_passing
         yield(self)
         self
       end
     end

I also define an 'in_passing' method for those times when you want to
preserve the input value yet process it for the side effects:

     1.with_self { |x| x + 1 }
     # returns 2

     1.in_passing { |x| p(x + 1) }
     # prints 2
     # returns 1

The thing is, I can't believe that something like this isn't already
built into Ruby.  I'm I overlooking it?

Thanks for your help.

Cheers,
Tom