Microsoft Word OpenIssuesInOO. doc

Block structure and multiple inheritance 

Block structure can sometimes be used as an alternative to multiple inheritance. In 

Reference [Øst90] it is shown how a common use of multiple inheritance for modeling 

windows with titles and borders may be handled using block structure. Since a window may 

have a title, a border or both, the following multiple inheritance class hierarchy is often 

used: 

---

Window

WindowWithTitle                                WindowWithBorde

WindowWithTitleAndBorder

 

This window hierarchy may be described using nested patterns: 

Window: 

 

(#  Title: (# ... #); 

 

 

Border: (# ... #); 

   ... 

 #); 

aWindow: @ Window(# T: @Title; B: @Border #) 

The descriptions for title and border are made using nested patterns. For a given window, 

like  aWindow, a title object and a border object may be instantiated. For example if two 

titles are needed, two instances of Title are made.