In CLOS, instance remorphing considered useless in practice?

[David McClain]

Just as an aside… that DSP prototyping environment still runs today as well as it did back in 2008 (perhaps a bit faster on todays CPUs). That is one thing about Common Lisp that I value highly. I have code that I wrote almost 30 years ago and have never needed to change, while it is still very much in use today.

I contrast that experience with programming in Rust just a year ago, while the entire language was changing beneath me almost monthly.

- DM

> On Dec 9, 2020, at 7:55 AM, dbm at refined-audiometrics.com wrote:
> 
>> Can I ask why you invoke #'CL:CHANGE-CLASS on an object instead of simply creating a new instance of the second class with adequate initialization?
>> 
> 
> I have used CHANGE-CLASS sparingly over the years. My first use was in a graphical DSP algorithm prototyping environment, and I believe it was related to graphical display objects. Almost a decade ago, so my memory is rusty.
> 
> But most recently I have a class hierarchy of objects, where some more refined subclass instances can act one way through an initial mixin class on their first execution of a principal method, and then revert back to other superclass behavior thereafter.
> 
> On CHANGE-CLASS, there is elision of slots in dropping back the the principal superclass structure. But every other slot remains intact. 
> 
> I cannot simply re-MAKE-INSTANCE on these objects as their identity is referenced in many places elsewhere. And what I need is a change in behavior, not identity. The only way to accomplish this change along the lines of re-making them, would require yet another layer of indirection. That might be interesting to contemplate.
> 
> - DM
> 
>