From: Clifford Heath <no@...>
Date: 2005-09-19T21:16:37+09:00
Subject: Metaprogramming problem

I'm trying to define s.t. like attr_accessor, but one that takes
an optional block defining a function that filters the value on
the setter. Perhaps that will be clear if I show you the snippet:

class Object
     def add_property(sym, &block)
         n = sym.id2name
         code = %Q{
             def #{n}()
                 @#{n} ||= nil
             end
             def #{n}=(value)
                 @#{n} = block ? block.call(value) : value
             end
         }
         eval(code)
     end
end

# A test object:
d = 3

# Add a getter and custom setter to 3:
d.add_property(:do_it) {|v|
     # Custom setter method
     puts "d.do_it here, v = #{v.inspect}"
     v	# No filtering this time, just return the value.
}

# Assign the property:
d.do_it = "a value"

Ok, I can see why "block" isn't defined. How can I pass add_property's
block in as a block to be used *inside* the evaluated code?

Clifford Heath.