如何忽略Common Lisp中的返回值

Question

I'm working with some code which calls ADJUST-ARRAY. I am getting a warning message from the Lisp interpreter (CMUCL) that the return value of ADJUST-ARRAY should not be ignored.

In the code I am working on, ADJUST-ARRAY modifies its argument in place, if I am not mistaken. So it's not necessary to do anything with the return value. Is there a designated way to ignore a return value in Common Lisp? Of course, I could assign the return value to some variable, and then ignore the variable. But that feels clumsy.

I could also assign the return value to the ADJUST-ARRAY argument, something like:

(setq my-array (adjust-array my-array ...))

but that seems to suggest that I'm not sure if ADJUST-ARRAY will modify MY-ARRAY in place.

Any advice is welcome, thanks in advance.

Answer 1

You are correct. As the documentation states:

The result is an array of the same type and rank as array, that is either the modified array, or a newly created array to which array can be displaced, and that has the given new-dimensions.

If the result is a newly created array then of course the function would have had no effect on the argument.

Common Lisp almost always require you to use the returned value rather than old bindings in order to have portable code.

Answer 2

The specification of adjust-array is that the adjusted array is the one returned.

What you can expect of the argument array afterwards to be is a bit complicated and may differ between implementations in some cases.

Just use the one returned. You might use setf to modify or let to create a binding.