Forum: Ruby Can you guess what it will be happened?

Announcement (2017-05-07): www.ruby-forum.com is now read-only since I unfortunately do not have the time to support and maintain the forum any more. Please see rubyonrails.org/community and ruby-lang.org/en/community for other Rails- und Ruby-related community platforms.
Jun Y. Kim (Guest)
on 2009-01-08 12:52
(Received via mailing list)
Hi. all

there are two array.

a = [1, 2]
b = [3, 4]

When I execute the following statement, what can you guess as a result?

irb:$> a.insert(a.length, *b)

very funny :)
Brian C. (Guest)
on 2009-01-08 13:06
It does exactly what I'd expect. The insert line expands to:

a.insert(2, 3, 4)  # a.length, b[0], b[1]

and so it inserts 3 and 4 at the end of the array. (It inserts before
element #n, but since a has only elements #0 and #1, asking to insert
before element #2 is the same as asking to insert at the end of the
list)

irb(main):001:0> a = [1,2]
=> [1, 2]
irb(main):002:0> b = [3,4]
=> [3, 4]
irb(main):003:0> a.insert(a.length, *b)
=> [1, 2, 3, 4]
irb(main):004:0> a
=> [1, 2, 3, 4]

Of course, a += b is a simpler way to write this.

Do you get something different? I am using ruby-1.8.6p114 under Ubuntu
Hardy.
Eustáquio Rangel (Guest)
on 2009-01-08 13:08
(Received via mailing list)
On Thu, Jan 8, 2009 at 8:51 AM, Jun Y. Kim 
<removed_email_address@domain.invalid>
wrote:
> Hi. all
> there are two array.
> a = [1, 2]
> b = [3, 4]
> When I execute the following statement, what can you guess as a result?
> irb:$> a.insert(a.length, *b)
> very funny :)

I didn't get the joke. :-)
Sebastian H. (Guest)
on 2009-01-08 13:22
(Received via mailing list)
Brian C. wrote:
> irb(main):003:0> a.insert(a.length, *b)
> => [1, 2, 3, 4]
> irb(main):004:0> a
> => [1, 2, 3, 4]
>
> Of course, a += b is a simpler way to write this.

Actually a.concat(b) is the simpler way to write this. a += b does
something
slightly different (create a third array [1,2,3,4] and then assign that
to a)
Brian C. (Guest)
on 2009-01-08 13:27
Sebastian H. wrote:
> Actually a.concat(b) is the simpler way to write this. a += b does
> something
> slightly different (create a third array [1,2,3,4] and then assign that
> to a)

Yes of course, sorry about that.

However I still don't see what the OP found funny...
Jun Y. Kim (Guest)
on 2009-01-08 13:27
(Received via mailing list)
thanks for your reply, brian.

what's the definition of '*'?

is this pointer?

I've never heard about "pointer" IN RUBY.

Am I wrong?

2009. 01. 08, ¿ÀÈÄ 8:06, Brian C. ÀÛ¼º:
Brian C. (Guest)
on 2009-01-08 13:34
Jun Y. Kim wrote:
> what's the definition of '*'?

That question was answered yesterday. See
http://www.ruby-forum.com/topic/175040
and follow the link to information on the splat operator.

> is this pointer?

No. You are probably thinking of C. Ruby is a different programming
language.

> I've never heard about "pointer" IN RUBY.

Me neither. But everything in Ruby is a reference, which is sort-of like
a pointer. But you don't do any explicit dereferencing like you would
for a pointer in C.
http://www.ruby-forum.com/topic/174962

> Am I wrong?

About what? That a.insert(a.length, *b) is somehow funny?
Sebastian H. (Guest)
on 2009-01-08 13:36
(Received via mailing list)
Jun Y. Kim wrote:
> what's the definition of '*'?
>
> is this pointer?

No, it's the "splat" operator. It expands an array into a list of
arguments.
So: foo(*[1,2,3]) == foo(1,2,3)  and  a.insert(2, *[3,4]) ==
a.insert(2,3,4)

HTH,
Sebastian
Eustáquio Rangel (Guest)
on 2009-01-08 13:47
(Received via mailing list)
Hi!

2009/1/8 Jun Y. Kim <removed_email_address@domain.invalid>:
> what's the definition of '*'?
> is this pointer?

It's called "splat operator". You can use it to "explode" your array
elements or join some variables on an array. Note the difference:

irb(main):001:0> a = [1,2]; b = [3,4]
=> [3, 4]
irb(main):002:0> a.push(b)
=> [1, 2, [3, 4]]
irb(main):003:0> a.push(*b)
=> [1, 2, [3, 4], 3, 4]

And now:

irb(main):004:0> def test(*args)
irb(main):005:1>   p args
irb(main):006:1>   end
=> nil
irb(main):007:0> test(1)
[1]
=> nil
irb(main):008:0> test(1,2,3)
[1, 2, 3]

Regards,
Jun Y. Kim (Guest)
on 2009-01-08 13:54
(Received via mailing list)
thanks for all your replies.

2009. 01. 08, 오후 8:46, Eustáquio Rangel 작성:
David A. Black (Guest)
on 2009-01-08 14:11
(Received via mailing list)
Hi --

On Thu, 8 Jan 2009, Eustáquio Rangel wrote:

> Hi!
>
> 2009/1/8 Jun Y. Kim <removed_email_address@domain.invalid>:
>> what's the definition of '*'?
>> is this pointer?
>
> It's called "splat operator". You can use it to "explode" your array
> elements or join some variables on an array. Note the difference:

AKA the "unary unarray" operator :-)


David

--
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Coming in 2009: The Well-Grounded Rubyist (http://manning.com/black2)

http://www.wishsight.com => Independent, social wishlist management!
This topic is locked and can not be replied to.