ExternView (3U)

#include <Unidraw/Components/externview.h>

ExternView is the abstract base class for external representation objects. Generally speaking, external representation objects convey domain-specific information outside the editor. They are simply component views that extract information from their subject and externalize it as a stream of bytes; thus the ExternView base class is derived from ComponentView.

There are three predefined ExternView subclasses: PreorderView, InorderView, and PostorderView. These subclasses manage subviews and support three common traversals of the external view hierarchy.

virtual boolean Emit(ostream&)

virtual boolean Definition(ostream&)

Emit and Definition make up the basic ExternView protocol. Emit initiates external representation generation and calls Definition on each of its children. Emit normally calls the external view's own Definition operation first. Then if the external view contains subviews, Emit invokes the children's Definition operations in the proper order to ensure a syntactically correct external representation. Both of these operation do nothing by default, and both return a boolean that indicates whether the stream of bytes was generated successfully.

ExternView* GetView(Iterator)

void SetView(ExternView*, Iterator&)

These operations do nothing by default. Subclasses that contain children should redefine them as follows: GetView should return the ExternView to which an iterator points. SetView should initialize the iterator to point to a particular ExternView in the list of children; it should initialize the iterator to point to a nil instance if the given ExternView is not a child.

ExternView(Component* = nil)

The abstract base class constructor is protected to guard against instantiation. It takes the subject as an optional argument.

PreorderView, InorderView, and PostorderView redefine their Definition operations to perform preorder, inorder, and postorder traversals of their children, respectively. Each child's Definition operation is called during the traversal. Note that every child must be an instance of the same ExternView subclass to ensure a consistent traversal order.

Component(3U), ComponentView(3U), Iterator(3U), ostream(3C++)