Non-symbols as keyword arguments

Zach Beane Common Lisp – Non-symbols as keyword arguments

Sometimes I like to have a short function call to make a lookup table with arbitrary keys and values. Something like this:

(table "name" "Alice" "age" 42) => #<TABLE ...>

This is easy enough to define like so:

(defun table (&rest keys-and-values)
   ;;; loop over keys and values to construct a table
   ...)

But there’s another option that works:

(defun table (&rest keys-and-values &key &allow-other-keys)
  ...)

This version has the advantage that missing arguments (e.g. (table "name")) are caught at compile-time!

I’ve been using this construct for a few years, but recently found out about 3.5.1.5, which says:

It is not permitted to supply a keyword argument to a function using a name that is not a symbol.

Yikes! That seems simple and straightforward: what I’m doing is not permitted. However! Every implementation I’ve tried (only three, admittedly) actually allows my not-symbol keywords without complaint!

I’m too old to think that “it works everywhere today” means “it will continue to work in SBCL tomorrow”, so I’m trying to figure out where I stand. 3.5.1.5 also says this:

If this situation occurs in a safe call, an error of type program-error must be signaled unless keyword argument checking is suppressed as described in Section 3.4.1.4.1 (Suppressing Keyword Argument Checking); and in an unsafe call the situation has undefined consequences.

So does that mean my code is:

• a safe call with suppressed keyword argument checking?
• …and is that good to use now and forever?
• an unsafe call with undefined consequences?
• something else?

I know the same effect could be achieved with a compiler macro, but I’d like to know if I can use this simpler option safely.