From: Robert Klemme <bob.news@...>
Date: 2005-10-03T04:41:46+09:00
Subject: Re: Eval and block problems

Brian Schr�der <ruby.brian@gmail.com> wrote:
> On 02/10/05, Ryan Leavengood <leavengood@gmail.com> wrote:
>> On 10/2/05, Brian Schr�der <ruby.brian@gmail.com> wrote:
>>> Please help me to wrap my mind around this. I want to achieve the
>>> following: [code snipped]
>>>
>>> and have the block from the dynamically created method foo be
>>> evaluated in the binding of the instance of A.
>>>
>>> I'm sure this is possible, but I've never really grocked eval,
>>> instance_eval and class_eval.
>>
>> Good question! Because by researching the answer I learned you can
>> just pass a block to define_method:
>>
>> class A
>>   def initialize(x)
>>     @x = x
>>   end
>>
>>   def self.def_me(cmd, &block)
>>     define_method(cmd, &block)
>>   end
>>
>>   def_me("foo") do
>>     puts "x is #@x"
>>   end
>> end
>>
>> A.new(1).foo
>> A.new(2).foo
>> __END__
>>
>> But strictly speaking in this case the separate def_me method is
>> redundant since you could just call define_method directly.
>>
>> Ryan
>>
>>
>
> Thank you ryan, it is incredible how fast there come really good
> answers here. Combining your proposal and davids I have the following.
> If I could get rid of the additional method, that would be perfect.

Just don't use the block for define_method but invoke it from the closure:

class A
  def self.def_me(cmd,&block)
    define_method(cmd) do
      puts "preparation"
      instance_eval &block
    end
  end

  attr_accessor :name
end

a=A.new
a.name = "Einstein"

A.def_me(:foo) do
  puts @name, self.name
end

>> a.foo
preparation
Einstein
Einstein
=> nil

Kind regards

    robert