From: Florian Gross <flgr@...>
Date: 2005-01-19T07:16:04+09:00
Subject: Re: value by reference

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Mohammad Khan wrote:

> Before telling my issue, let me show my script:
> 
> def do_something(a, b, c)
>     a = a + 1
>     b = b + 2
>     c = c + 3
> end                                                                                                                                      
> a, b, c = 5, 6, 7
>                                                                                                                                                         puts "before do_something:"
> I would like to see the value of a, b, c after calling #do_something as:
> a = 6, b = 8, c = 10
> 
> how can I do it without making a, b, c an instance variable?
> In other words, how can I send value by reference?

This is not easily done. First of all you should ask yourself why you 
find yourself needing it and if there is not a better mechanism in Ruby 
that you could use to accomplish your goal. (Methods can return multiple 
values.)

After that there's two approaches to addressing the above:

1) Supply lambdas:

def do_something(inc_a, inc_b, inc_c)
   inc_a.call(1)
   inc_b.call(1)
   inc_c.call(1)
end

do_something(
   lambda { |x| a += x },
   lambda { |x| b += x },
   lambda { |x| c += x }
)

2) Use variable.rb to handle variables as Objects:

def do_something(a, b, c)
   a.value += 1
   b.value += 1
   c.value += 1
end

do_something(Variable[:a], Variable[:b], Variable[:c])

If you find yourself really needing to do this, please follow up with 
your reasons. I've not yet found many cases where this is necessary and 
would be interested in getting to know about new ones.

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