Re: force initialization of a datatype?

[Dmitry Gutov]

On 11/04/2015 06:28 PM, Stephen Leake wrote:

> (defun make-path-iterator (<user args>)
>    (let ((result (vector 'cl-struct-path-iterator <slot values>)))
>      <code to check the user args and set the slots in `result'>
>      ))
>
> This code compiles and runs correctly, but I'm wondering if it is
> acceptable style. Is there a better way to accomplish this for
> cl-defstruct?

Using `vector' looks wrong. I'm not too familiar with constructor 
syntax, but you can process each slot value before an instance gets 
constructed. See the example with &aux in 
http://www.gnu.org/software/emacs/manual/html_node/cl/Structures.html, 
or package-desc-from-define in package.el.

I'm not sure whether you can use a keyword argument with the same name 
as the slot, and convert the passed in value. That's something to try.

> eieio defclass provides ":initform", which I'm guessing can specify a
> function to run at object construction time, but I can't find any
> definitive statement to that effect, neither in the Emacs info doc nor
> via DuckDuckGo search. The lack of good documentation scares me away
> from eieio in general.

If we're talking about xref, I think it would be generally good to 
migrate away from eieio in the core definitions. defstruct is lighter, 
and seems functional enough for our purposes.