how to use setf_last

Hi Laurent,

The whole point of the setf_* helper functions/macros is to allow the simple use of setf(place value) and then this is transformed into the right function with maybe more cryptic syntax. For example:

expandMacroDeep('(setf (car (last A)) "e"))
car(rplaca(last(A) "e"))

You could (I guess) use setf_last directly, but you need to remember that last() is a list - so you'd need to use (setf_last (list "e") A) - note the arguments are also the opposite way around than you were using.

I would strongly suggest you use setf rather than directly calling the helper function.

Andrew

Hi Laurent,

The whole point of the setf_* helper functions/macros is to allow the simple use of setf(place value) and then this is transformed into the right function with maybe more cryptic syntax. For example:

expandMacroDeep('(setf (car (last A)) "e"))
car(rplaca(last(A) "e"))

You could (I guess) use setf_last directly, but you need to remember that last() is a list - so you'd need to use (setf_last (list "e") A) - note the arguments are also the opposite way around than you were using.

I would strongly suggest you use setf rather than directly calling the helper function.

Andrew

Thanks for the prompt reply.
I missed the point in the doc about the reversed arguments for the helper functions!
I'll follow your suggestion

Not sure it's going to help you memorize it but if you were to build a self helper, you will realize that in a self_helper the value to set can only be the first argument.

If you have a fancy getter function : 

(defun fancy_getter ( positional_arg @optional optional_arg @rest args ) "Return whatever value" ... )

To build a self_helper for it, you need to take all the getter arguments but also the value to set which is a necessary argument.

The only way to make it necessary is to start with it. It will look like this : 

(defun setf_fancy_getter ( value positional_arg @optional optional_arg @rest args ) "Set whatever value and return it" ... )

BTW you can also use defsetf to associate the update function (the helper) with the access function. Doesn't particularly make it easier to understand though ;-)

Andrew