When to use * arguments?

ruby-talk
1

version one:

def say(*a)
  a.each {|r| puts r }
end

say(1,2,3)

···

------

version two:

def say(a)
  a.each {|r| puts r }
end

say([1,2,3])
-------
So, any different here? when should we * arguments like version one?
--
Posted via http://www.ruby-forum.com/.

2

version one:

def say(*a)
  a.each {|r| puts r }
end

say(1,2,3)
------

version two:

def say(a)
  a.each {|r| puts r }
end

say([1,2,3])
-------
So, any different here? when should we * arguments like version one?

* is useful when you don't know the number and kind of arguments the method
will receive. Using * will convert any arguments to an Array.

In your first version:

  > say 123
  123
  [123] <-- returns an Array

In your second version:

   > say 123
   NoMethodError: undefined method `each' for 2:Fixnum
        from (irb):6:in `say'

···

El Viernes, 8 de Enero de 2010, Zhenning Guan escribió:
  
--
Iñaki Baz Castillo <ibc@aliax.net>

3

Hi,

version one:
  def say(*a)
    a.each {|r| puts r }
  end
  say(1,2,3)

version two:
  def say(a)
    a.each {|r| puts r }
  end
  say([1,2,3])

So, any different here? when should we * arguments like version one?

Sometimes you have to use splats: when you call another method and
you don't know what arguments that one takes. Object.new does this
internally. It's something like

  class Object
    class <<self
      def new *args
        instance = allocate_space
        instance.initialize *args # <<<
        instance
      end
    end
  end

Bertram

···

Am Freitag, 08. Jan 2010, 18:43:41 +0900 schrieb Zhenning Guan:

--
Bertram Scharpf
Stuttgart, Deutschland/Germany
*
Support `String#notempty?': <http://raa.ruby-lang.org/project/step&gt;\.

4

To nitpick (I know it isn't relevant to the discussion at hand), it's actually
more something like:

class Class # instance method of Class, not singleton method of Object
   def new *args, &blk # Can take (and will pass) a block, too
     # Calls Class#allocate (or a particular class's override of that method)
     instance = allocate
     instance.send(:initialize, *args, &blk) # initialize is a private method
     instance
   end
end

Except, of course, it's written in C.

···

On 08.01.2010 13:00, Bertram Scharpf wrote:

It's something like

class Object

> class <<self
> def new *args
> instance = allocate_space

instance.initialize *args # <<<

> instance
> end
> end
> end