Clascal Reference Manual Mar83

CLASCAL REFERENCE MANUAL for the LISA 1N First Dratt~ March· 9th , MCMLXXXIII by Da.vid Casseres IApple Co"puter. Inc. 198J Cla.sca1 Reference ManuaJ CONTENTS 1 Introduction to Clascal Concepts 1.1 Class-Types ....•..... 1.2 Objects ............ . 1.3 The Class H1erarchy .... . 1.4 ~~ce ........... . 1.5 Assignment-Compa;tibillty of Objects Expa.ns1on ofEx1st1ng Pasca.1. Syntax .. 'Def1rdng a Class .......................... . l)ef'ining a Metl\.od . • • • • • • . . . • . • • • • . • . • • • . • • • • . .......... 2 3 4 4.1 4.2 4.3 4.4 4.5 4.6 5 6 'l OverrldingInher1tedMethods ••• Self-Reference via. the Self Pseudova.ria.ble Self-Reference via a Class-Identif1er Cla.sswid.e Methods Abstra.ctMethods • The New Metl\.od Class Object .•••••. Objects as Handles ...... . $H+ a.n.d$H- Compiler Commands Appendix A:· Sample lJstings ............. . 1 1 1 . . •. 2 2 3 3 •. 6 9 9 9 11 13 13 14 14 15 16 A-l Reference Manual Cla.sca.J 1 Introduction to Clascal Concepts Clascal is a set of extensions to Pascal on the Lisa. These extensions support "object-oriented" programming in a style th.a.t somewhat resembles SIMULA and SmalltaJk. The purpose is to provide a very highlevel interface to code libraries, allowing the user program to perform highly complicated functions with simple eaJ.ls, while still reta.irrlng flexibility . 1.1 Class-Types Cla.sealis ba.sed on a new category of user-def1ned types called clasS'" types. An individual class-type is referred to as a aJass. A cla.ss-type is a klnd of S'trUctured-type, resembling a reeord-type in that it contains na.med fields. A class can have two kinds of fields: • 1)8,:ta. Oelds are like the fields of a record; they. contain variable data, and each data field has its own type. • .Methods are procedures and functions. The fields are referenced lUte fields of a record, using a period and a field-identlf1er (or a w1th-statement that references a. field-identlf1er). For' exa.mple, it. area. identi:f1es a· field· defined in class Triangle, and c:rntTria:ngleis decla:rec:1 by va.r c:rntTr.ia.ngle: Tr.ia.ngle; then crntTrla.ngle. 8J'."e& is a reference to the area. field of cri\.tTrla.ngle. If azea. is a data. field, then crntTr.ia.ngle. area. is a va.ria.ble-referen.c:e; if area. is a. method, then crntTrla.ngle.area. is either a proceduresta.ternent or a. :t\mction-ca.ll. A class-type is declared in the interface-part of a unit, and is supported by a .method-block in th.eimplementation-part of the same unit. Section 3 gives the syntax for class-types and method-blocks. 12 Objects A class defines the behavior (data. fields and methods) of its objects:. Each objeetis an .tnsta.nce of the class tha.t def1nes its behavior. Each object is stored. in a. dyn~ca.lly alloca.ted.,pot.entially reloeatable data area. w1th,1n a heap. An. object of a given class is created by the new method defined. for that class; .this method returns a newlY created object of the cl.a.ss(see Seetl.on <4.6). …