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Combine 3.12 (Default branch)
11-19-2008
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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)