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comp.lang.ruby

* before string

Jonatas Paganini

2/12/2009 4:51:00 PM

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.
--
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6 Answers

Bertram Scharpf

2/12/2009 5:22:00 PM

0

Hi,

Am Freitag, 13. Feb 2009, 01:51:24 +0900 schrieb Jonatas Paganini:
> 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


--
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-...

Robert Klemme

2/12/2009 5:26:00 PM

0

On 12.02.2009 17:51, Jonatas Paganini wrote:
> 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?

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 DeNatale

2/12/2009 5:56:00 PM

0

[Note: parts of this message were removed to make it a legal post.]

On Thu, Feb 12, 2009 at 12:22 PM, Bertram Scharpf
<lists@bertram-scharpf.de>wrote:

> Hi,
>
> Am Freitag, 13. Feb 2009, 01:51:24 +0900 schrieb Jonatas Paganini:
> > 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.


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.denh...
Twitter: http://twitter.com/Ri...

7stud --

2/12/2009 6:30:00 PM

0

Jonatas Paganini 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


--
Posted via http://www.ruby-....

7stud --

2/12/2009 6:43:00 PM

0

7stud -- wrote:
> Jonatas Paganini 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

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7stud --

2/12/2009 6:49:00 PM

0

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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