Forum: Ruby * before string

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Jonatas P. (Guest)
on 2009-02-12 18:52
Hi, I'm looking for cucumber/generators and didn't understand why use
'*' before string on initialize method.
I put it on irb and the result is the same.

class NamedArg
    attr_reader :name

    def initialize(s)
      @name, @type = *s.split(':')
    end
end

Why and where use * before string?

thanks.
Bertram S. (Guest)
on 2009-02-12 19:24
(Received via mailing list)
Hi,

Am Freitag, 13. Feb 2009, 01:51:24 +0900 schrieb Jonatas P.:
> class NamedArg
>     def initialize(s)
>       @name, @type = *s.split(':')
>     end
> end
>
> Why and where use * before string?

Actually, you use the asterisk in front of an array. The asterisk
makes the array to a list of arguments. Examples:

  ary.push [ :a, :b]     # pushes an array
  ary.push *[ :a, :b]    # pushes two symbols

You may even do this:

  done = %(exit quit bye)
  case str.downcase
    when *done then return
  end

In your example, the conversion will be done automatically when
the right side is an array. When I code, I write the asterisk
explicitly every time to remind myself what I meant.

Bertram
Robert K. (Guest)
on 2009-02-12 19:32
(Received via mailing list)
On 12.02.2009 17:51, Jonatas P. wrote:
> end
>
> Why and where use * before string?

It's not before a String but before an Array.  You can see for yourself
by firing up IRB and experimenting a bit with this.  The short story is
that it's called "splash operator" IIRC and it will distribute the Array
across all parameters or local variables.  Other example uses are

def foo(a,b,c)
   puts a,b,c
end

foo(1,2,3)
ar = [1,2,3]
foo(*ar)
foo(ar) # -> error because you do not provide enough arguments

HTH

Kind regards

  robert
Rick D. (Guest)
on 2009-02-12 20:09
(Received via mailing list)
On Thu, Feb 12, 2009 at 12:22 PM, Bertram S.
<removed_email_address@domain.invalid>wrote:

>
>    when *done then return
>  end
>
> In your example, the conversion will be done automatically when
> the right side is an array. When I code, I write the asterisk
> explicitly every time to remind myself what I meant.


All true, except that in this case, it's in the context of a parallel
assignment statement rather than a method call.


--
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
7stud -. (Guest)
on 2009-02-12 20:31
Jonatas P. wrote:
>
>       @name, @type = *s.split(':')
>
> Why and where use * before string?
>

Your statement is equivalent to:

@name, @type = *(s.split(':') )

Here is a simple example:

arr = ["apple", "banana"]
x, y = *arr
puts x, y

--output:--
apple
banana


Or:

s = "hello world"
x, y = *s.split()
puts x, y

--output:--
hello
world
7stud -. (Guest)
on 2009-02-12 20:44
7stud -- wrote:
> Jonatas P. wrote:
>>
>>       @name, @type = *s.split(':')
>>
>> Why and where use * before string?
>>
>
> Your statement is equivalent to:
>
> @name, @type = *(s.split(':') )
>

...and it looks like the * is redundant:

x, y = ["snowboard", "skis", "sled"]
puts x, y

--output:--
snowboard
skis
7stud -. (Guest)
on 2009-02-12 20:49
And apparently you can do this:

x, y, *remaining = ["snowboard", "skis", "sled", "boots"]

puts x, y
p remaining

--output:--
snowboard
skis
["sled", "boots"]
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