Re: Map iteration and modification

["Randy Brukardt" <randy@rrsoftware.com>]

"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.)

               Randy.