From: Ken Bloom <kbloom@...>
Date: 2006-12-07T00:55:06+09:00
Subject: Re: Default values for method arguments

On Wed, 06 Dec 2006 07:27:00 -0800, paul wrote:

>> You just need to switch strategies.  Use Ruby's simulated keyword
>> arguments for something like this:
>>
>>  >> def test(args)
>>  >>   puts args.values_at(:a, :b, :c)
>>  >> end
>> => nil
>>  >> test :a => 1, :c => 2
>> 1
>> nil
>> 2
>> => nil
> Hi James,
> 
> The Simulated Keyword Arguments you talk about are a little abstract to
> me, but I think I get the idea. I suppose in the example above I would
> have to add a couple of lines to define the default values...
> This way, the general idea is the same as the following?
> 
> irb(main):001:0> def test(args)
> irb(main):002:1>   args['a'] = 'defaultA' unless args.has_key?('a')
> irb(main):003:1>   args['b'] = 'defaultB' unless args.has_key?('b')
> irb(main):004:1>   args['c'] = 'defaultC' unless args.has_key?('c')
> irb(main):005:1>   puts args.indexes('a', 'b', 'c')
> irb(main):006:1> end
> => nil
> irb(main):007:0> test({'a' => 'someA', 'c' => 'someC'})
> (irb):5: warning: Hash#indexes is deprecated; use Hash#values_at
> someA
> defaultB
> someC
> => nil

Try this-- it's more concise, and you probably won't feel the need
for more syntactic magic after that.

def test(args)
  args[:a] ||= 'defaultA'
  args[:b] ||= 'defaultB'
  args[:c] ||= 'defaultC'
  puts args.indexes(:a, :b, :c)
end

> 
> An additional question: do you know a link where I can find more on
> those Simulated Keyword Arguments? I did some googling, but it turned
> up with nothing on:
> ruby "Simulated Keyword Arguments"
> 
> Those colons you use before the variable-names are a little like magic
> to me. (though I checked, without those colons, you're example above
> wouldn't have worked...) :)

The colons make them into symbol objects.

> Cheers,
> Paul




-- 
Ken Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/