[Oorexx-devel] 'self' in class methods: bug or feature ?

[Rony G. F. <Ron...@wu...>]

In the context of an assignment for a student (creating a frameword for
vCalendar and vCard) the following concept has been developed:

    * create a root class with a class attribute "attr" and "values"
      which both will get array values from subclasses, that determine
      the attributes which should be created for the subclasses (using
      the 'define' method) in this class' class constructor,
    * create for each vCard type a subclass with a class constructor,
      that first assigns array objects  to the root class' class
      attributes "attr" and "values" which denote the attribute names
      which this class instances should have.

The problem:

    * 'self' in class methods is not set to the class object for which a
      class method executes, as is the case for 'self' in instance
      methods. Rather 'self' will refer to the class object for which
      the class method got defined. Because of this it is not possible
      to create the attributes dynamically in the root class class
      constructor!

A stripped down example program from that student, sketching the problem:

    /* b2.rex */
    say "-"~copies(50)
    L = .LIST~OF(.ADR)
    DO CLZ OVER L
    	SAY "Defined methods for instances of" pp(CLZ)":"
    	DO IDX OVER CLZ~METHODS(clz)~ALLINDEXES~SORT
    		SAY pp(IDX)
    	END
    	SAY "-------"
    END

    /*
    ----------------------------------------------------------------
    CLASS DEFINITION OF VCARD VERSION 3.0
    */

    ::CLASS VCARD30 PUBLIC
    ::ATTRIBUTE ATTR CLASS --ATTRIBUTE USED IN SUBCLASSES

    /* INIT METHOD THAT CREATES MAKER AND SETTER METHODS FOR ATTRIBUTES */
    ::METHOD INIT CLASS ; --TRACE ?I
    say "VCARD30::"self": INIT CLASS, self~attr="pp(self~attr)

       if \self~attr~isA(.array) then return

    say "VCARD30::"self": defining ATTR-attributes:"

       -- create attributes (getter and setter methods) for instances
    	DO NAME OVER SELF~ATTR
    say "... defining:" pp(name) pp(name"=")
    		SELF~DEFINE(NAME, MAKEGETTER(NAME))
    		SELF~DEFINE(NAME||'=', MAKESETTER(NAME))
    	END



    ::METHOD INIT
    --TRACE ?I
    	ATTR = SELF~CLASS~ATTR --ASSIGNS NEWLY CREATED ATTRIBUTES
    	VALUES = SELF~CLASS~VALUES


    	DO NAME OVER ATTR
    		SELF~SEND(NAME||"=",.ARRAY~NEW) --SETS INITIAL ATTRIBUTE-VALUES TO AN ARRAY
    	END


    /*
    ----------------------------------------------------------------
    CLASS DEFINITION OF ADR
    FURTHER DETAILS RFC 2426, P. 11, 31
    */
    ::CLASS ADR PUBLIC SUBCLASS VCARD30
    ::METHOD INIT CLASS

    say pp("ADR::"self)": INIT CLASS, top: self~attr="pp(self~attr)
    /*
    ATTRIBUTE AND VALUE VARIABLES OF CLASS
    */
    --TRACE ?I
    	SELF~ATTR = .ARRAY~OF("TYPE", "TEST_ATTRIBUTE")

    say pp("ADR::"self)": INIT CLASS, bottom: self~attr="pp(self~attr)

    	FORWARD TO (SUPER)


    ::METHOD INIT
    --TRACE ?I
    	FORWARD TO (SUPER) CONTINUE



    /* ================================== routines ================================= */
    /* enclose argument's string value in square brackets */
    ::routine pp
      parse arg val
      return "["val"]"

    /*
    ROUTINE CREATES A GETTER METHOD FOR ATTRIBUTES
    */
    ::ROUTINE MAKEGETTER
    	PARSE ARG NAME
    	CODE="EXPOSE" NAME "; RETURN" QUOTE(NAME)
    	RETURN CODE

    /*
    ROUTINE CREATES A SETTER METHOD FOR ATTRIBUTES
    */
    ::ROUTINE MAKESETTER
    	PARSE ARG NAME
    	CODE="EXPOSE" NAME "; USE ARG" NAME
    	RETURN CODE

    /*
    ROUTINE SURROUNDS VARIABLES WITH DOUBLE QUOTES
    */
    ::ROUTINE QUOTE
    	PARSE ARG VALUE
    	RETURN '"'||VALUE||'"'

      

Running the above program yields the following output:

    VCARD30::The VCARD30 class: INIT CLASS, self~attr=[ATTR]
    [ADR::The ADR class]: INIT CLASS, top: self~attr=[ATTR]
    [ADR::The ADR class]: INIT CLASS, bottom: self~attr=[an Array]
    VCARD30::The VCARD30 class: INIT CLASS, self~attr=[ATTR]
    --------------------------------------------------
    Defined methods for instances of [The ADR class]:
    [INIT]
    -------
      

Because of this it is not possible to take advantage of the inheritance
behaviour and make it easy to complete the creation of classes at
runtime using class constructors. Giving dozens of types in the
vCalendar and vCard standards, implementing this at each subclass level
means that a lot of hand-coding and/or copying must take place. This is
not needed at the instance level, and as class objects are "normal
objects" there should be no exception there. Conceptually, I would
therefore think that this is a bug. But before filing a bug, I would
like to learn whether this is a feature, and if so, what the reasoning
would be.

---rony