Re: Incorporating caching into defgroup/defcustom/defvar for Emacs 25

[Sean Allred <code@seanallred.com>]

Actually, I’ve just read a message from Artur on the matter:

> The way I see it, emacs has a great interface for persistent customizable options (defcustom) and it has defvar for internal non-persistent variables. But it doesn't have anything for internal persistent variables. You can call custom-save-variable on an internal variable, but then it's up to you to check the value on initialization, and it's also a little awkward to use this for very large variables (since they'll clog up the user's custom-file, which is probably also the init file). That's why several packages (ido, bookmark, etc) end up manually writing/reading variables to/from disk. 
> 
> Thus, there's clearly the need for stashes, persistent internal variables. These are not customizable variables, because we already have defcustom for that.
> However, similar to a defcustom, a defstash also belongs to a group. This grouping is not used for customization (stashes don't show up in the customize interface), but it is used to group stashes in the file system. Each group corresponds to a subdirectory, and all stashes from that group go in that directory. This would be specified by passing the :stash-directory keyword to defgroup. This keyword (and one or two others) would be the only changes necessary outside the stash.el file. 
> 
> Obviously, groups with no stashes will not have a directory. Also, groups with only one or two stashes may opt to not use a subdirectory. 


Specifically, his point about defcustom is a good one. Such variables shouldn’t be cached in the same sense. stash.el was and is designed as a patch for the lack of “internal persistent variables”. The additional keyword(s?) to defgroup and a defvar* macro would suffice.

Best,
Sean