From: Thomas Gantner <thomas.gantner@...>
Date: 2007-08-26T05:40:45+09:00
Subject: Re: accessor_writer methods and instance_eval

on Fri 24. August 2007 03.30, Nobuyoshi Nakada wrote:

> Hi,
> 
> At Fri, 24 Aug 2007 08:40:08 +0900,
> Thomas Gantner wrote in [ruby-talk:266021]:
>> Is there a way to avoid this behaviour without using 'self.a' or passing
>> the struct as a parameter into the block (which quite obsoletes the
>> meaning of instance_eval)?
> 
> Nothing.  It's one of reasons why using instance_eval for such
> purpose is not a good idea.
> 

Thanks for your quick answer (also to Ezra).

I found a solution by defining setter-methods for every struct member:

  class C
    def initialize(&blk)
      @format = Struct.new( ... many, many elements ...) do
        members.each do |key|
          self.send(:define_method, "set_#{key}".to_sym) do |new_value|
            self[key] = new_value
          end
        end
      end
      @format.instance_eval(&blk) if block_given?
    end
  end

Then I can use:

  c = C.new { set_elem8(8); set_elem17('test'); ... }

Quite readable, but not many keystrokes saved. Is there a better
alternative? I understand you suggest something without instance_eval()?

-Thomas

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