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devel / comp.lang.tcl / Understanding Tcl memory management of list created in C

Understanding Tcl memory management of list created in C

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https://www.novabbs.com/devel/article-flat.php?id=9898&group=comp.lang.tcl#9898

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Subject: Understanding Tcl memory management of list created in C
Date: Tue, 25 Oct 22 16:58:40 GMT
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by: clt.to.d...@dfgh.net - Tue, 25 Oct 2022 16:58 UTC

>From: Harald Oehlmann <wortkarg3@yahoo.com>
>Date: Tue Oct 25 10:07:16 GMT 2022
>Subject: Understanding Tcl memory management of list created in C

Another interesting nitpick

set B [list {*}$lA]

is about twice as fast as:

lappend B {*}$A

for long lists on my machine, and does not assume B starts empty, or does not yet exist.

In any case I can think of, a fast and safe way to copy a long list (saved in A), then append "zzz" to the copy (while saving the original list in A) would be:

set B $A
lappend B zzz

In this case the first step is very fast (copying a pointer to the original list), and the second is slow (because the original list is duplicated by Tcl's internal copy on write logic before it is modified). Which is very close to Gertjan's thoughts on relative timings.

Dave B

Subject	Author
Understanding Tcl memory management of list created in C	clt.to.davebr