Self-interest November 2003

self-interest@lists.selflanguage.org

13 participants
14 discussions

Issues about delegation
by "J. Baltasar García Perez-Schofield" 07 Nov '03

07 Nov '03

Hi, there ! I've some doubts about a language employing only delegation as its inheritance mechanism. Perhaps these doubts are simple and are answered elsewhere (probably in some self paper I should study), or perhaps I'm even missing something big. Anyway, I would like to have some feedback about this. Suppose a system which includes a compiler for a protoype-based object-oriented language, with single inheritance, implemented through delegation. Suppose you have a prototype such as this one (please let me use an [imperative, classic, C++/Java-like] pseudo-code): OBJ Person ATR Parent Object ATR Name "" MTH getName MTH putName ... ENO So, therefore, the object Person derives from the root prototype object (called Object here), and has only one atributte (for the shake of simplicity), called "Name" which should store a String (i.e., a copy of the String prototype, which is the name of the person). If you want to create persons, then you just copy them. The system is in charge of copying their attributes (so, each person will have its own name, because the attributes (except "parent") are copied recursively). Here I suppose this is done by calling a "clone" method which is actually defined in "Object" (so the method look up runs throgh the "Parent" atributte). joe = Person.clone(); mary = Person.clone(); joe.putName("Joe"); mary.putName("Mary"); Console.write(joe.getName()); // Writes "Joe" Console.write(mary.getName()); // Writes "Mary" So far, so good. But I don't know how a language such as this one would cope with prototypes derived from "Person". For example: OBJ Employee ATR Parent Person ENO It it semantically correct - ane employee is a class of person -, and it would work employing a concatenation mechanism for inheritance. If you create two objects: joe2 = Employee.clone(); mary2 = Employee.clone(); joe2.putName("JOE"); mary2.putName("MARY"); Console.write(joe2.getName()); // Writes "MARY" Console.write(mary2.getName()); // Writes "MARY" These two objects, joe2, and mary2, share the shame String, because both objects have a "parent" attribute pointing to Person. Worst of all, joe2 and mary2 are actually modifying a prototype (an object which is playing the role, in this case, of a class). How can I solve this ? Of course I can think of some work arounds, such as recreating the "name" atribute in Employee, or using a composition relation instead of the inheritance one, but I think this should be possible to be solved whithin inheritance/delegation. Thank you in advance, j.Baltasar ======================================= PBC - J. Baltasar García Perez-Schofield Dep. Informática, Universidad de Vigo, España (Spain)

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Self UI question
by Steve Dekorte 06 Nov '03

06 Nov '03

When clicking on an method slot, a method inspector opens containing the source code for the method. How do you then actually inspect the method *object* then? Likewise for Strings, etc. -- Steve

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Problems running Self on a IBook
by Friedrich Dominicus 06 Nov '03

06 Nov '03

running under MacOS X. Installation works but the opening screen says Version 4.1.5 (although I downloaded the 4.2 version is that still ok?) I can start the Demo with Self -s Demo.snap and I can navigate on the screen but I can not use my keyboard, it simply does not work. It just beeps. There are a few things I do not understand. I git a few warnings and other messages on the console here's an except: Self VM warning: _allocatd went negative Self VM warning: A one-work branch may not span the gap from the .... Self VM warning: ignoring failed Aple even: , -1708 VM version: 4.1.10 ?? Self 5 finger: Mac: no such user finger: unkown host: this sigchild ignored Well I do not no what the messages mean but obviously something is wrong. Does anyone have encountered simular problems and/or does someone know a work around? Regards Friedrich

2 4

summary of Dave's oopsla talk
by Jecel Assumpcao Jr 05 Nov '03

05 Nov '03

John McIntosh has a nice "trip report" about OOPSLA, which includes this page describing Dave Ungar's invited talk: http://www.smalltalkconsulting.com/html/OOPSLA2003d4.html -- Jecel

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Self-interest November 2003