Ability to define custom destructorings

[yyoncho]

At this point, dash supports 4 different destructoring keyword (keys/hash/plist/alist) and from what I can see it will be not hard to add new keywords by providing a destructuring template(or macro?) to generate the getter.

Example usecases:

• &hash which checks whether the map is empty before applying gethash
• Custom destructuring for cl-defstruct, e. g.

(-let [(&my/struct slot1 slot2) value]
  ...)

[Fuco1]

Hi Ivan. This is something I haven't considered but it shouldn't be terribly difficult as you say. One would need to make sure the recursive expansions would still work, but so long as you do not publish your custom getter I guess the contract is your own.

The place to start at would be in the function dash--match in the second condition (consp match-form). Before the default case we can add something that would look at the symbol's property (using get) dash--matcher or something similar and execute that.

Would you be interested in trying to implement this (does what I said make any sense at all? :))

[yyoncho]

I have checked the code upfront, just wanted to know whether you are going to accept such PR - check #277 . I have not updated the docs if this is needed.

[yyoncho]

@Fuco1 is there a change to move this issue forward? In lsp-mode we are want to support both maps and alists and we are going to replace gethash with map-elt but we still do not have a solution for &hash destructoring. We spent a lot of time to migrate our code to use dash and it will be a pity if we now have to rewrite it again to use pcase-let or something like that.

[Fuco1]

@yyoncho I will merge this today, I promise!

[yyoncho]

Thank you @Fuco1 . Not sure whether it is ready for merging though (e. g. it lacks documentation).