Re: [TCLCORE] Agressive shimmering

[Joe E. <jen...@fl...>]

Don Porter wrote:
>
> Remember that [string length] returns the number of characters in
> the string.  That information is not stored anywhere in the Tcl_Obj struct.
>
> (objPtr->length is in bytes, not chars)
>
> The shimmer happens so that we have someplace to store the computed
> length in chars, so when it's asked for again we don't have to compute
> it again.


I wonder if that's worth revisiting for novem (or possibly earlier).

I have a hunch that in many (most?) real programs, the UCS-2
representation never pays off -- [string length] is only
amortized O(1) if you call it a lot :-) the first one still
costs O(n).

>From a quick scan through the manpages, it looks like [string length],
[string range], [string index], [string replace], and the regexp operations
are the main things that algorithmically benefit from a UCS-2 representation.
Pretty much everything else can be implemented just as efficiently
on UTF-8.  (For that matter so can all the regexp operations,
if we're willing to replace the Spencer engine.)



--Joe English

 * * *

... Well, there's also [string reverse], but if that's ever been used
outside of "How fast can *your* language reverse a string?" shootouts
I've yet to see it.