DEFCLASS

A defclass is a construct for specifying the properties (slots) of a class of

objects. A defclass consists of four elements: 1) a name, 2) a list of

superclasses from which the new class inherits slots and message-handlers,

3) a specifier saying whether or not the creation of direct instances of the

new class is allowed and 4) a list of slots specific to the new class. All

user-defined classes must inherit from at least one class, and to this end

COOL provides predefined system classes for use as a base in the derivation

of new classes.

Any slots explicitly given in the defclass override those gotten from

inheritance. COOL applies rules to the list of superclasses to generate a

class precedence list for the new class. Facets further describe slots.

Some examples of facets include: default value, cardinality, and types of

access allowed.

The syntax of the defclass construct is:

(defclass <name> [<comment>]
  (is-a <superclass-name>+)
  [<role>]
  [<pattern-match-role>]
  <slot>*
  <handler-documentation>*)

<role>  ::= (role concrete | abstract)

<pattern-match-role> 
        ::= (pattern-match reactive | non-reactive)

<slot>  ::= (slot <name> <facet>*) |
            (single-slot <name> <facet>*) |
            (multislot <name> <facet>*)

<facet> ::=  <default-facet> | <storage-facet> |
             <access-facet> | <propagation-facet> | 
             <source-facet> | <pattern-match-facet> |
             <visibility-facet> | <create-accessor-facet>
             <override-message-facet> | <constraint-attributes>
 
<default-facet> ::= 
           (default ?DERIVE | ?NONE | <expression>*) |
           (default-dynamic <expression>*)

<storage-facet> ::= (storage local | shared)

<access-facet> 
       ::= (access read-write | read-only | initialize-only)

<propagation-facet> ::= (propagation inherit | no-inherit)

<source-facet> ::= (source exclusive | composite)

<pattern-match-facet> 
       ::= (pattern-match reactive | non-reactive)

<visibility-facet> ::= (visibility private | public)

<create-accessor-facet> 
     ::= (create-accessor ?NONE | read | write | read-write)

<override-message-facet> 
     ::= (override-message ?DEFAULT | <message-name>)
                                           
<handler-documentation> 
       ::= (message-handler <name> [<handler-type>])

<handler-type> ::= primary | around | before | after