Path: news.daimi.aau.dk!news.uni-c.dk!sunic!sunic.sunet.se!news.luth.se!eru.mt.luth.se!news.kth.se!nac.no!Norway.EU.net!EU.net!howland.reston.ans.net!news.sprintlink.net!pulm1.accessone.com!usenet From: Baiss E. Magnusson Newsgroups: comp.lang.beta Subject: Overriding procedural patterns Date: 1 May 1995 16:10:20 GMT Organization: PDI Lines: 27 Distribution: world Message-ID: <3o315c$9he@pulm1.accessone.com> NNTP-Posting-Host: 204.118.152.121 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Newsreader: Nuntius 2.0_68K X-XXDate: Mon, 1 May 1995 17:09:18 GMT I am troubled by the Beta definition that a virtual pattern can only be extended and cannot be completely redefined. The complete over-riding of the enclosing procedure pattern seems to me to be a fundamental need. My experience with object oriented applications is that one of the most common uses of class hierarchies is the notion of a selected set of items. An operation, for instance , is performed on that selected set. The operation of drawing in a lower class will not use the same drawing commands as the object in a super class. Consider the following class hierarchies, all taken from real world application programs: 1) Pre-press Application: Signature - Press sheet - Page - Page crop mark 2) CAD Application: Symbol - Irregular polygon - line 3) Word Processing Application: Page - Paragraph - word In all cases the user selects a grouping of both higher and lower objects, (i.e. a press sheet and a page ) and then moves the objects. The first thing that is done is a "function message" is sent to every object in the group to draw to an off screen map. Then the map is moved. The draw function of the page will not do all the things that the draw function of the press-sheet does. Is this not possible in Beta? It would be in Simula.