classes(3U)                                                 InterViews Reference Manual                                                classes(3U)

NAME

       classes - unique identifiers for catalog-managed objects and component views

SYNOPSIS

       #include <Unidraw/classes.h>

DESCRIPTION

       Classes  for  catalog-managed  objects,  including components, commands, tools, state variables, and transfer functions, must be associated
       with mutually-unique class identifiers that can be written onto disk.  This allows a creator object to call the appropriate constructor  as
       part of recreating an object from disk.

       Also,  there  must be a mechanism for creating an appropriate view given a subject; that is, there must be an association between a subject
       class and allowable view classes for that subject.  This association is established by defining  class  identifiers  for  component  views.
       These identifiers are formed by concatenating the identifier for a given component subject class with an identifier that specifies a ``view
       category.''  For example, the class identifier for the PostScript external view of a line component is the concatenation of the  identifier
       for  the  line  component subject class and POSTSCRIPT_VIEW identifier, which specifies the category of external views for generating Post-
       Script.  This makes it possible to create an instance of the appropriate PostScript external view subclass given a line component subject.

       The class identifiers for the Unidraw base and predefined derived classes are specified in the classes.h include file.   Applications  that
       define  new  catalog-managed  objects or component views should define unique class identifiers in a similar manner.  Class identifiers for
       catalog-managed objects are simply integers with mnemonic macro definitions, usually the class name in  all-uppercase.   For  example,  the
       identifier for the LineComp component subject class is

       #define LINE_COMP 9030

       View  class  identifiers are specified using the Combine macro, which takes as its first argument the macro definition of the corresponding
       component subject identifier; its second argument is an identifier for the view category.  The Combine macro itself is then defined with  a
       mnemonic  name.   For example, the identifier for the PostScript external view class PSLine (which generates PostScript for the line compo-
       nent subject) is defined as

       #define PS_LINE Combine(LINE_COMP, POSTSCRIPT_VIEW)

       where the POSTSCRIPT_VIEW view category identifier is defined as

       #define POSTSCRIPT_VIEW 9103

       N.B.: All class identifiers in a given application must be unique.

SEE ALSO

       Catalog(3U), Creator(3U)

Unidraw                                                            12 June 1990                                                        classes(3U)