From: Robert Klemme <shortcutter@...>
Date: 2006-08-28T18:10:20+09:00
Subject: Re: Fun with setter functions

On 26.08.2006 16:42, Jan Svitok wrote:
> On 8/26/06, Kevin Olbrich <devlists-ruby-talk@devlists.com> wrote:
>> I have a setter function in a class that I would like to pass additional
>> arguments to, so I can do some addtional calculations if required.
>>
>> My first crack at this was to do something like...
>>
>> ....
>> def variable=(value, options=nil)
>>   @variable = value
>>   do_something_cool if options == :flag
>> end
>>
>> Here's the only problem, how do you pass the options?
>>
>> object.variable = value, :flag
>> results in
>> [value, :flag] being passed to the function.
>>
>> I see a couple of work arounds.
>> 1. send works, but is ugly  object.send('variable=',value,:flag)
>> 2. rewrite variable so that it expects an array and just unpack stuff
>> from the array
>>
>> Any other solutions I may have overlooked?
> 
> Try
> 
> def variable=(*args)
>  @variable = args.shift
>  do_something_cool if args.shift == :flag
> end
> 
> *args will receive array of arguments passed in either case (i.e. both
> when one and two parameters are passed)
> 
> The latter args.shift will return nil if there are no more parameters.
> 
> Another possibility could be using hash parameters, as rails often does:
> 
> def variable=(value, options ={})
>   @variable = value
>   do_something_cool if options[:options] == :flag
> end
> 
> Call as: variable = value, :options => :flag

Both approaches won't work as Ruby does allow only exactly one argument 
to an assignment:

11:06:12 [Temp]: cat -n var.rb
      1
      2  class Foo
      3    def var=(val,*opts)
      4      p opts
      5      @var = val
      6    end
      7
      8    def var() @var end
      9  end
     10
     11  f=Foo.new
     12  p f.var
     13  f.var = 10
     14  p f.var
     15  f.var = 10, 20
11:06:18 [Temp]: ruby var.rb
nil
[]
10
[]

You can get it to work with send but then you're loosing the clean syntax:

11:07:03 [Temp]: cat -n var.rb
      1
      2  class Foo
      3    def var=(val,*opts)
      4      p opts
      5      @var = val
      6    end
      7
      8    def var() @var end
      9  end
     10
     11  f=Foo.new
     12  p f.var
     13  f.var = 10
     14  p f.var
     15  f.var = 10, 20
     16  p f.var
     17  f.send(:var=, 10, :opt => 20)
11:08:08 [Temp]: ruby var.rb
nil
[]
10
[]
[10, 20]
[{:opt=>20}]
11:08:08 [Temp]:

Kind regards

	robert