Passed by reference for an octave_value type storing an external resource?

[Olaf Till]

Hi,

by this post

https://mailman.cae.wisc.edu/pipermail/help-octave/2012-November/054991.html

I learned that there are Octave Forge packages storing external
resources (e.g. descriptors for open serial, parallel, or i2c devices)
in classes derived from octave_base_value hooked into
octave_value.rep, which are then passed to user space as Octave
variables of a newly created type. These Octave variables are then
used as arguments providing the descriptor to various user-called
functions of the package. Example:

octave-forge/main/i2c/serial/serial_class.h, /serial_class.cc,
/serial.c, /srl_close.cc.

To keep track whether the resource is open or closed, the returned
value of .get_rep() of the passed octave_value is casted to non-const
with a C-style cast and then a change is made within .rep (e.g. in
srl_close.cc).

JWE, when I suggested the latter for a previous attempt of yours to
treat Comedi-related resources conceptually similar to the above
package, you discouraged casting away const this way.

(thread: 
https://mailman.cae.wisc.edu/pipermail/octave-maintainers/2008-November/013305.html)

But what is the actual danger in it, as long as

- users can't change values of this type except using functions
  provided by the package,

- functions provided by the package never make copies, but make each
  change within the existing .rep?

(I'm trying to achieve an agreement on a strategical suggestion for
such problems.)

Olaf

-- 
public key id EAFE0591, e.g. on x-hkp://pool.sks-keyservers.net

signature.asc
Description: Digital signature