Can you guess what it will be happened?


#1

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 :slight_smile:


#2

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.


#3

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 :slight_smile:

I didn’t get the joke. :slight_smile:


#4

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)


#5

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…


#6

thanks for your reply, brian.

what’s the definition of ‘*’?

is this pointer?

I’ve never heard about “pointer” IN RUBY.

Am I wrong?

    1. 08, ¿ÀÈÄ 8:06, Brian C. ÀÛ¼º:

#7

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


#8

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?


#9

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,


#10

thanks for all your replies.

    1. 08, 오후 8:46, Eustáquio Rangel 작성:

#11

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 :slight_smile:

David


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