From: Robert Klemme <bob.news@...>
Date: 2006-02-22T22:03:32+09:00
Subject: Re: Syntax questions

listrecv@gmail.com wrote:
> A few simple syntax questions:
>
> 1) Anyway to do use the default arg for nonlast params?  Something
> like:
> run(xyz, , 3)

No.  You have to use one form of keyword arguments (for example by using a 
hash).  Note that proper support for this is likely to happen in Ruby 2.0.

> 2) Veru often I see things like:
> a, b = meth()
> Is meth returning two objects?  Or is it returning one object - like a
> tuple or something - which the parser automagically splits into a & b?
> What are the rules of using two vars with commas together?

It's a combination of parallel assignment with multiple return values.

# parallel assignment
a,b,c=1,2,3
a,b,c=[1,2,3]

# multiple return values
def mu1
  return 1,2,3
end

def mu2
  [1,2,3]
end

def mu3
  return [1,2,3]
end

irb(main):015:0> a,b,c = mu1
=> [1, 2, 3]
irb(main):016:0> a
=> 1
irb(main):017:0> b
=> 2
irb(main):018:0> c
=> 3
irb(main):019:0> a,b,c = mu2
=> [1, 2, 3]
irb(main):020:0> a
=> 1
irb(main):021:0> b
=> 2
irb(main):022:0> c
=> 3
irb(main):023:0> a,b,c = mu3
=> [1, 2, 3]
irb(main):024:0> a
=> 1
irb(main):025:0> b
=> 2
irb(main):026:0> c
=> 3

The star operator can be used to collect remaining args:

irb(main):029:0> a,*b = mu1
=> [1, 2, 3]
irb(main):030:0> a
=> 1
irb(main):031:0> b
=> [2, 3]

More strictly speaking, returning anything that implements #to_ary will be 
treated this way:

irb(main):032:0> class Foo
irb(main):033:1> def to_ary() ["foo",2,3] end
irb(main):034:1> end
=> nil
irb(main):035:0> def foo() Foo.new end
=> nil
irb(main):036:0> a,b,c = foo
=> ["foo", 2, 3]
irb(main):037:0> a
=> "foo"
irb(main):038:0> b
=> 2
irb(main):039:0> c
=> 3

HTH

Kind regards

    robert