Re: (copy-marker nil)

["Andreas Röhler" <andreas.roehler@easy-emacs.de>]

On 07.05.2018 15:39, John Mastro wrote:
> Andreas Röhler <andreas.roehler@easy-emacs.de> wrote:
>> being surprised WRT behavior of copy-marker:
>>
>> (setq a (copy-marker nil)) -> #<marker in no buffer>
>> (markerp a) -> t
>> a -> #<marker in no buffer>
>>
>> Is taking nil by copy-marker reasonable?
>>
>> Wanted to check for a valid buffer position, which doesn't seem
>> possible that way. While without copy-marker, the variable a would be
>> set to nil, now the result evaluates to #<marker in no buffer>, which
>> is a kind of t.
> 
> There are other ways to get a marker to no buffer, such as
> 
> (let ((a (point-marker)))
>    (set-marker a nil))
> 
> So if you don't control the creation of the marker, it's probably a
> scenario you need to take care for either way.
> 
> Explicitly testing the marker's buffer should work:
> 
> (let ((a (copy-marker nil)))
>    (and (markerp a)
>         (buffer-live-p (marker-buffer a))))
> 

Thanks. A way to deal with ;)