RE: [External] : Use of an associated list with completing-read

[Drew Adams <drew.adams@oracle.com>]

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> >     (setq-local tema-lugar
> >                 (append tema--lugar (list (cons lnum strg))))
> 
> This is the classic recipe for poor scaling performance since the above
> operation takes time proportional to the length of the list, so if you
> execute this N times (in a loop), the loop builds a list of length N
> but takes time N² to do it.  When N is small, noone notices, and as it gets
> large the performance starts to suck.

Heime:

One programming cliche for this is to
(1) start with a list that you create
(e.g., a let-binding to nil), so you
don't modify any existing list that
you might not want to mess with, (2)
use `nconc' instead of `append', to
append quickly (the _list structure_
is modified - destructive), (3) being
sure to set your list variable to the
result of each modification.

An even more common cliche for doing
the same thing is to do #1, then (2)
cons instead of append, and (3) when
finished adding list elements, do an
`nreverse' of the list you created.
That too is a destructive operation.

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