From: ts <decoux@...>
Date: 2008-05-06T01:07:09+09:00
Subject: Re: String copy-on-write question

Lars Christensen wrote:

 Well, it's best if you look at rb_str_substr() in string.c

>    str[100..-1]  # this costs only a small amount of memory

 ruby just need to adjust the pointer and the length in the new
 object 

>   str[100..-2]   # this costs around 16MiB bytes of memory

 one character is missing from the previous string, if it do the
 same thing than previously then it must
  * adjust the pointer
  * adjust the length
  * add \0 at the end

 This mean that fatally it has modified the string, this is why it
 duplicate.

>   p $'.size  # This is free
>   p $`.size  # This costs another 8MiB.

 same reason here.


Guy Decoux