From: Robert Klemme <shortcutter@...>
Date: 2008-05-06T01:20:08+09:00
Subject: Re: String copy-on-write question

On 05.05.2008 18:07, ts wrote:
> 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.

Interesting.  Do you also happen to know why not an additional field is 
used that stores the length?  Is the reason maybe usage of C library 
string functions that work on zero terminated strings?

Cheers

	robert