Can you guess what it will be happened?

[Jun Young Kim]

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 Candler]

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]

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 Hungerecker]

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)

 

[Jun Young Kim]

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, =BF=C0=C8=C4 8:06, Brian Candler =C0=DB=BC=BA:

 

[Brian Candler]

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...

 

[Brian Candler]

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 Hungerecker]

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]

Hi!

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 Young Kim]

thanks for all your replies.

2009. 01. 08, =EC=98=A4=ED=9B=84 8:46, Eust=C3=A1quio Rangel =EC=9E=91=EC=84=
=B1:

Hi!

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 =3D [1,2]; b =3D [3,4]
=3D> [3, 4]
irb(main):002:0> a.push(b)
=3D> [1, 2, [3, 4]]
irb(main):003:0> a.push(*b)
=3D> [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
=3D> nil
irb(main):007:0> test(1)
[1]
=3D> nil
irb(main):008:0> test(1,2,3)
[1, 2, 3]

Regards,