Overriding subclass method in squeak

Question

I need to make a new subclass method to a new classs that i created who got 2 class instance varribles : isInterface and behavesLike. i need to make a subclass method that gets this parameters as well and creates a new sub class with thos parameters. i just cant get what am i doing wrong here . this is my code :

subclass: aSubclassName isInterface: isInterface behavesLike:
    aCollection instanceVariableNames: instVarNames classVariableNames:
    classVarNames poolDictionaries: poolDictionaries category:aCategoryName
|m|
    m:=(super subclass: aSubclassName
        instanceVariableNames: instVarNames
        classVariableNames:classVarNames
        poolDictionaries: poolDictionaries
        category: aCategoryName).
(m class) instVarNamed:'behavesLike' put:aCollection;instVarNamed:'isInterface' put:isInterface
            ^(m class).

i just keep getting those errors :

score 1 · Accepted Answer · answered Dec 19 '17 at 17:06

You are mixing class and instance level, a very frequent issue.

Classes are artifacts that create instances. And instVars are, precisely, in the instances. In your case,

(m class) instVarNamed:'behavesLike' put:aCollection

attempts to set the instance var of a class, because m class is a class. If you want an instance, you should talk to m class new, but even worse, because m itself is a class, so m class is a metaclass. To understand all this confusion, you should read the chapters about Metaclasses in the Blue Book. But to fix your code, m new instead of m class should work

Overriding subclass method in squeak

1 Answers1