Re: `append' vs. `nconc'

[Pascal J. Bourguignon]

Emanuel Berg <embe8573@student.uu.se> writes:

> OK, so for example this:
>
> (setq completion-ignored-extensions
>       (append completion-ignored-extensions '(".bcf" ".run.xml")) )
>
> Is better as:
>
>     (nconc completion-ignored-extensions (list ".bcf" ".run.xml"))
>
> ?

No.  You should never use nconc only for effect (just like delete, etc).

Always re-assign the modified list:

    (setf completion-ignored-extensions
          (nconc completion-ignored-extensions (list ".bcf" ".run.xml")))

otherwise it will break when the place is bound to nil.  (nil is a symbol
and cannot be mutated into a cons cell!).

-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
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