[lnkForumImage]
TotalShareware - Download Free Software
Confronta i prezzi di migliaia di prodotti.
Asp Forum
 Home | Login | Register | Search 


 

Forums >

comp.lang.ruby

Question about string's in-place modification

Sam Kong

6/4/2005 7:06:00 PM

Hello!

I wonder how destructive methods work in the behind.

For example,

s = '12345'
s2 = s
s.sub!('3', 'three')
puts s #->'12three45'
puts s2 #->'12three45'

Destructive methods are in-place.
Does that mean the object doesn't change its location in memory?
Probably not.
I don't think it's possible as the object might need more space and
need to move to a bigger empty space for the changed data.
If it moves, the references pointing to it should be updated as well.

How exactly does that work?

Thanks in advance.
Sam
4 Answers

Gennady

6/4/2005 7:56:00 PM

0

Just look into string.c in Ruby distribution. It's open source, after
all ;-).

Gennady.

On Jun 4, 2005, at 12:10, Sam Kong wrote:

> Hello!
>
> I wonder how destructive methods work in the behind.
>
> For example,
>
> s = '12345'
> s2 = s
> s.sub!('3', 'three')
> puts s #->'12three45'
> puts s2 #->'12three45'
>
> Destructive methods are in-place.
> Does that mean the object doesn't change its location in memory?
> Probably not.
> I don't think it's possible as the object might need more space and
> need to move to a bigger empty space for the changed data.
> If it moves, the references pointing to it should be updated as well.
>
> How exactly does that work?
>
> Thanks in advance.
> Sam
>
>

dblack

6/4/2005 8:11:00 PM

0

Tim Hunter

6/4/2005 8:19:00 PM

0

Sam Kong wrote:
> Hello!
>
> I wonder how destructive methods work in the behind.
>
> For example,
>
> s = '12345'
> s2 = s
> s.sub!('3', 'three')
> puts s #->'12three45'
> puts s2 #->'12three45'
>
> Destructive methods are in-place.
> Does that mean the object doesn't change its location in memory?
> Probably not.
> I don't think it's possible as the object might need more space and
> need to move to a bigger empty space for the changed data.
> If it moves, the references pointing to it should be updated as well.
>
> How exactly does that work?
>
> Thanks in advance.
> Sam
>

Don't think of an object's id as a memory address. Think of it as a
handle for a memory address. That way, if the memory address of an
object needs to change (if, for example, Ruby needs to allocate more
memory for a string) Ruby can update the id with the new address and the
id can remain the same.

Lothar Scholz

6/4/2005 9:04:00 PM

0

Hello Sam,

SK> Hello!

SK> I wonder how destructive methods work in the behind.

SK> For example,

SK> s = '12345'
SK> s2 = s
SK> s.sub!('3', 'three')
puts s #->>'12three45'
puts s2 #->>'12three45'

SK> Destructive methods are in-place.
SK> Does that mean the object doesn't change its location in memory?
SK> Probably not.
SK> I don't think it's possible as the object might need more space and
SK> need to move to a bigger empty space for the changed data.
SK> If it moves, the references pointing to it should be updated as well.

SK> How exactly does that work?

A string is of c type VALUE (as every ruby object). This c type hold
at least 16 byte. So there is enough space to keep a string length and
the pointer inside the object.


SK> Thanks in advance.
SK> Sam




--
Best regards, emailto: scholz at scriptolutions dot com
Lothar Scholz http://www.ru...
CTO Scriptolutions Ruby, PHP, Python IDE 's