From: Nilesh Trivedi <nilesh.tr@...>
Date: 2009-09-10T22:23:54+09:00
Subject: Re: defining a singleton method dynamically

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Thanks Davind. That makes sense. :)

cheers
nilesh
http://nileshtrivedi.in

On Thu, Sep 10, 2009 at 6:26 PM, David A. Black <dblack@rubypal.com> wrote:

> Hi --
>
> On Thu, 10 Sep 2009, Nilesh Trivedi wrote:
>
>  On Thu, Sep 10, 2009 at 6:05 PM, Nilesh Trivedi <nilesh.tr@gmail.com>
>> wrote:
>>
>>  How do I define a singleton method dynamically?
>>>
>>> I have code similar to this:
>>>
>>> def foo(obj,label)
>>>  def obj.name; label; end #we want to define a singleton method called
>>> "name" on obj which returns the value in label
>>>  puts obj.name #this is an example. Actually I have some code here which
>>> expects this singleton method in obj
>>> end
>>>
>>> When I try to run this as foo(Object.new,"xyz"), it throws a "NameError:
>>> undefined local variable or method `label' for #<Object:0xb7b02018>"
>>> whereas
>>> I want it to print "xyz" to screen.
>>>
>>> Of course, line 2 in method foo is not correct. But what is the correct
>>> way?
>>>
>>>
>> Replacing line 2 by:
>>
>> obj.instance_eval "def name; '#{label}'; end"
>>
>> does get the behaviour that I want. Is this the best way to do this or is
>> there a better, cleaner way?
>>
>
> It may be overkill, but I pretty much always choose the block form of
> *_eval rather than the string form, as per my response of a couple of
> minutes ago. If you're going to eval strings, you could also do:
>
>  eval "def obj.name; '#{label}'; end"
>
>
>
> David
>
> --
> David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com
> Ruby/Rails training, mentoring, consulting, code-review
> Latest book: The Well-Grounded Rubyist (http://www.manning.com/black2)
>
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>
>

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