Re: eieio defclass evaluate :initform value

[Eric Abrahamsen <eric@ericabrahamsen.net>]

Joe Riel <joer@san.rr.com> writes:

> On Wed, 04 Jan 2017 12:45:22 -0800
> Eric Abrahamsen <eric@ericabrahamsen.net> wrote:
>
>> Joe Riel <joer@san.rr.com> writes:
>> 
>> > According to the info page for eieio for Emacs 23, one
>> > could do
>> >
>> > (defclass foo-class
>> >    ((bar :initform (lambda () my-var)
>> >          :type string)))
>> >
>> > When make-instance was called, the lambda expression
>> > for :initform would be evaluated and the expression
>> > assigned to my-var would be used for the slot bar.
>> >
>> > The info page for eieio Emacs 24 does not mention this 
>> > functionality and testing shows it no longer exists.
>> >
>> > Is there nice way, in 24, to create a class with an :initform
>> > that, upon instantiation, evaluates to the value of a variable?
>> 
>> Depending on what exactly you want, you might be able to solve it with
>> `oset-default', which lives outside the class definition, and can
>> evaluate variables. See if that does what you want?
>
> Thanks, Eric; I wasn't aware of oset-default and could use it, however,
> am currently taking a different approach.  The bigger picture is that
> I'm using a buffer-local object to store configuration data for a
> major mode.  The object is normally updated when the mode is invoked,
> but the global defaults should be configurable.  The current approach
> is to clone a default object whose values can be assigned via a 
> customization.  The documentation for using defcustom with an eieio object
> is slim, but I got it working.

Yup, that would be awkward to do with `oset-default'. Glad you got
something working.

Eric