From: dblack@...
Date: 2007-07-12T01:31:58+09:00
Subject: Re: Catching what a block returns (A newbie lesson learned)

Hi --

On Thu, 12 Jul 2007, Richard Lawrence wrote:

> Realizing that "yield" evaluates to something I can assign to variables, etc. 
> was important for getting beyond the trivial examples.  In retrospect, I 
> should have paid more attention to the lesson that *everything* evaluates in 
> Ruby.  I think what I was hung up on is that "yield" is a keyword (right? at 
> least it looks like one), and hence I thought of it as mere flow control, not 
> a passage for information.

I'm pleased you worked this out, and it does indeed point you to a
great deal of yield's coolness.  And you're right that keyword
expressions, too, always evaluate to something (with the exception of
return, since doing this:

   x = return 1

would at best just discard x).  It's true even for class and method
definitions: class definition blocks evaluate to the last expression
inside them, and def blocks evaluate to nil.  So this:

   class C
     def m
     end
   end

evaluates to nil, while this:

   class C
     1
   end

evaluates to 1.  (And yes, this feature does actually get used in
slightly more real situations :-)


David

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