Re: [Emacs-diffs] master c13a4df: Remove the calls to `seq-into` from `seq-concatenate`

[Stefan Monnier <monnier@iro.umontreal.ca>]

>>> Yes, it is still a problem.  One solution would be to test if the seq is
>>> a cl-struct with, in which case we could use `seq-into'.  But then that
>>> would only fix the cl-struct case, not any other.
>> If we make it into a defmethod, at least it would be possible for
>> specific cl-structs to fix the problem.
> It is already, or did you mean something else?  But how would you do it
> here?  There can be any number of sequences.

That's exactly the issue: it needs to be structured so that callers can
usefully override it.

As it is currently defined, the only overriding possible is to provide
new valid values for the `type' argument.

So its default definition should make use of seq-into or something
similar so that new types can provide their own implementation.
E.g., you could define a new

  (cl-defgeneric seq-into-sequence (seq)
    (if (sequencep seq) seq
      (error "Don't know how to turn %S into a sequence" seq)))

and then

  (cl-defgeneric seq-concatenate (type &rest seqs)
    (apply #'cl-concatenate type (mapcar #'seq-into-sequence seqs)))


        Stefan