From: Arlen Cuss <celtic@...>
Date: 2008-03-09T08:47:12+09:00
Subject: Re: A question on singleton methods

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Hi Mike,

On Sun, Mar 9, 2008 at 10:34 AM, mike leonard <mikeleonard@gmail.com> wrote:

>    def a_hash.fetch(:a).to_s
>        "ALPHA"
>    end
>

The problem here is that you can't involve a method call/dispatch (or two)
in the method definition. "a_hash.fetch(:a).to_s" has to make at least one
method call (a_hash.fetch(:a)), and then one defines the method on the
resulting object. Method definitions don't work this way (they need to be
resolvable in the current context, I believe). But there's a way to get
there:

>> a ={:a => "q"}
=> {:a=>"q"}
>> b = a[:a]
=> "q"
>> a[:a].object_id
=> -606856898
>> b.object_id
=> -606856898
>> def b.some_method
>> puts "Hi."
>> end
=> nil
>> b.some_method
Hi.
=> nil
>> a[:a].some_method
Hi.
=> nil
>>

By the by, I'm not sure redefining a String's #to_s will have any effect. It
sounds strange - perhaps you're better off building a class for those
objects and defining to_s on that?

Cheers,
Arlen

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