Re: safe_call1 considered harmful

[Kenichi Handa <handa@m17n.org>]

In article <E1G5548-0002HD-8x@fencepost.gnu.org>, Richard Stallman <rms@gnu.org> writes:

>     find-operation-coding-system calls a registered function
>     with a single argument; a list of arguments given to
>     find-operation-coding-system.  So, appending an extra
>     argument at the tail of the list is fairly safe.

> It might seem that way; but what happens if we change the calling
> convention of one of the operations, giving it an additional argument?
> That may be necessary some day.  I prefer the current convention.

We can change tar-mode/arc-mode/jka-compr to call
find-operation-coding-system with full number of arguments
plus the extra argument BUFFER.  Then, a function called
from find-operation-coding-system can check if the number of
arguments is greater than the normal number (which can be
checked by subr-arity).  If it is greater, the function can
know that the last argument is BUFFER.  By that way, the
function doesn't break even if we add a new argument to
find-operation-coding-system.

---
Kenichi Handa
handa@m17n.org