From: Mohammad Khan <mkhan@...>
Date: 2005-01-19T07:37:42+09:00
Subject: Re: value by reference

On Tue, 2005-01-18 at 17:16, Florian Gross wrote:
> 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.)
> 

I really need it.
I could do it by: 

def do_something(a, b, c)
  a = a + 1
  b = b + 2
  c = c + 3
  return [a , b, c]
end

a, b, c = do_something(a, b, c)

I don't like to handle with too many return variables but I had to do it
in my real project.



> 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 }
> )

What is lambdas? sorry.. if I am asking anything very strange !!
I will still prefer to return multiple variables in stead of using these
much code!


> 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.