From: Aaron Janes <ruby-forum@...>
Date: 2006-03-10T02:36:49+09:00
Subject: Error calling block in sub class

I am creating a base collection class that will allow the assignment of 
multiple code blocks which validate the addition of objects to the 
collection.  The code looks like this:

<< Code Snippet >>

class CollectionBase
  public
    def initialize()
      @validators = Array.new() # Contains any validators
      @items = Array.new() # Contains collection's objects
    end

    # Adds a code block to the validators array that will be called when 
adding
    # items to the collection.
    def add_validator(&block)
      validators.push(block)
    end

    # Adds an object to the collection
    def add(obj)
      # Check to see if the object is valid for this collection
      if valid?(obj)
        @items.push(obj)
        return @items.length - 1
      end
    end

... Code omitted to be consise

    # Loops through all validators and passes the
    # object being checked to the code block.
    # If any validator returns false the object is
    # invalid.
    def valid?(obj)
      invalid = false
      @validators.each do |validator|
        if !validator.nil?
          invalid = true if !validator.call(obj)
        end
      end
      !invalid
    end
end

<< End Code Snippet >>

This code works fine.  I can create a new CollectionBase, pass a code 
block to add_validators and depending on the result of the code block 
objects are added or not.

The problem comes when I try and subclass this class.  I also want to 
create a SetBase class which extends CollectionBase but by default adds 
a validator that prevents duplicate objects from being added:

<< Code Snippet >>

require 'Collections'

class SetBase < CollectionBase
  public
    def initialize()
      super
      # add a validator that returns false if object is already
      # in the set
      add_validator {return !index(obj) }
    end
end

<< End Code Snippet >>

When I try to add an item to SetBase, however, I get the error:
   unexpected return (LocalJumpError)

I have stepped through with a debugger and the error is raised when an 
attempt is made to call the code block (ie. the addition of the 
validator works fine).

Does anyone have any idea why this is happening?

Thanks,
Aaron

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