From: "Pieter V." <pvande@...>
Date: 2007-05-20T04:38:53+09:00
Subject: Block Trouble (Binding Issue?)

I'm presently trying to work on a little metaprogramming project, but
am finding my efforts a little frustrated by ... well, I'm not rightly
sure what by.  It seems to be a scoping issue, from what I can tell.

Here's a sample case:

############
class BlockTester
  def x
    "Correct Method!"
  end

  def self.x
    "WRONG METHOD!"
  end	

  def self.meth(name, &b)
    # ... do some stuff
    define_method name, &b
  end

  def self.normal_meth(name, &b)
    meth(name, &b)
  end

  def self.special_meth(name, &b)
    meth(name) do
      # do something special
      yield # <= This is the problematic call
    end
  end
end

# Test Case

class Foo < BlockTester
  meth "foo" do x end
  normal_meth "bar" do x end
  special_meth "baz" do x end
end

f = Foo.new
f.foo # => "Correct Method!"
f.bar # => "Correct Method!"
f.baz # => "WRONG METHOD!"
############

The goal, as may not be immediately apparent from the code, is for
"special_meth" to be able to create a new method that automatically
executes a few lines of code before executing the block.  While this
is similar in principle to overriding a method in a subclass...

############
class X
  def to_s
    "green" + super
  end
end
############

... I can't seem to make this very common pattern stick for a block.
Any suggestions?