Re: should search ring contain duplicates?

[Juri Linkov]

> I think that for most uses of a history it makes no sense to keep
> duplicates. I'd vote for making the default value be t and letting those few
> modes where duplicates might make sense (e.g. shell-mode?) bind it to nil
> unless the user has explicitly specified otherwise.
>
> IOW the option values could be:
>
>  nil            - means never remove duplicates
>  t (default)    - means remove duplicates, but this can be
>                   overridden by a mode (e.g. shell-mode)
>  non-nil, non-t - means always remove duplicates (never override)
>
> This would require code changes only for those few modes that want to
> override the default (t). Plus a change to the defcustom.

A related feature that specifies the maximum length of the history list
uses the `history-length' _property_ of the history list _symbol_
to override the default value of the _variable_ `history-length'
for a particular history list.  Exactly the same thing could be
implemented for `history-delete-duplicates', i.e. the property
`history-delete-duplicates' would override its default value
for a particular history list.

-- 
Juri Linkov
http://www.jurta.org/emacs/