Donal K. Fellows skrev:
>  Larry McVoy wrote:
> > Can you explain that a bit?  I'm thinking something like
> >
> >     when we detect a foreach (c in buf) 
> > 	bump the refcount on buf
> > 	set an index at 0
> > 	start the loop
> > 	each iteration
> > 		c = buf[index++]
> > 		loop body
> > 		decr refcount on c
> >         decr refcount on buf
> >
> > What's so hard about that?  I realize I'm asking this naively so I'm not
> > say "you wuss, go do it", I'm say "teach me why this is hard, please".
>  
>  The problem is that lots of code has to be rewritten to understand
>  keeping a reference count on the buffer, or rather on the string rep[*].
[snip]
>  [* Some of our strings have internal representations that allow us to
>      process them much more efficiently. This was important for avoiding
>      the costs that would otherwise be incurred from using UTF-8, and was
>      the main way that we recovered from the slowdown in Tcl 8.1... ]

Just verifying that I understood this correctly, because your 
objections sounded really strange on a first read-through. Is it true that:
1. It's not possible to iterate over the String intRep like this, 
unless one reimplements it to have a separate refcount, because 
shimmering could cause it to go away.
2. The same problem exists for bytearray intReps.
3. It would be possible to iterate over the string representation 
*bytes instead, because that cannot go away unless the value is 
modified. (An earlier remark "index into buf?  Module unicode char 
widths, etc." by Larry gave me the impression he intended to iterate 
over UTF-8 encoded data.)

?

Lars Hellström

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