Using Common Lisp CLOS objects as keys in a hashtable?

Question

I\'d like to use Common Lisp CLOS objects as keys in a hashtable. I thought it would be as simple as this:

(defclass my-class () ((a :accessor a :initarg a)))

         


        

Answer 1

Common Lisp standard does not provide any mechanism to provide additional test functions (beyound standard ones). You have 2 options:

1. Use genhash genhash which is portable hash-table implementation (not compatible with built-in ones)
2. Use non-standard extensions:
   1. SBCL has sb-ext:define-hash-table-test function (documentation)
   2. Clisp has a similar function ext:define-hash-table-test (documentation)
   3. Allegro ans Lispworks accept non-standard values for :test argument and has :hash-function argument (Allegro, Lispworks).