Re: Map iteration and modification

[DrPi <314@drpi.fr>]

Le 30/12/2023 à 07:29, Randy Brukardt a écrit :
> "DrPi" <314@drpi.fr> wrote in message
> news:ummj1i$e64$1@rasp.pasdenom.info...
> ... (Example eliminated)
> 
>> That's what I did but I saved the keys (String) instead of the cursors.
>> Does it make a difference ? Performance maybe ?
> 
> It certainly will make a performance difference; whether that difference is
> significant of course depends on the implementation. There's two parts to it
> (one of which I thought of yesterday and the other which I forgot):
>     (1) The cost of storing keys vs. storing cursors. Cursors are going to be
> implemented as small record types (cannonically, they are two pointers, one
> to the enclosing container and one to the specific node/element). A key can
> be most anything, and storing that can be more costly.
>     (2) The cost of looking up a key. A map is a set of nodes, and there
> needs to be some operation to associate a key with the correct node. Those
> operations take some time, of course: for a hashed map, the key has to be
> hashed and then some sort of lookup performed. Whereas a cursor generally
> contains an indication of the node, so the access is more direct.
> 
> For a lot of applications, this difference won't matter enough to be
> significant. But I'd probably lean toward using cursors for this sort of job
> as that would minimize performance problems down the line. (Of course, if
> the container gets modified after you save the cursors, then they could
> become dangling, which is a problem of it's own. If that's a possibility,
> saving the keys is better.)
> 
I modified my code to use cursors.
Thanks for your help.

Nicolas