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From: niklas@appli.se (Niklas Hallqvist)
Newsgroups: comp.lang.c++
Subject: Re: solution to implementing parameterized classes
Message-ID: <1393@appli.se>
Date: 15 Jun 91 06:54:31 GMT
References: <1991Jun9.013306.4462@cs.sfu.ca> <1991Jun9.204515.18040@ms.uky.edu> <25349@well.sf.ca.us> <1991Jun11.183133.11458@auto-trol.com> <14976@exodus.Eng.Sun.COM>
Organization: Applitron Datasystem AB, GOTHENBURG, SWEDEN
Lines: 40

chased@rbbb.Eng.Sun.COM (David Chase) writes:

>mattel@auto-trol.com (Matt Telles) writes:

>>nagle@well.sf.ca.us (John Nagle) writes:
>>> As does the notion that "(void *)" should be a normal part of programming.

>>  FINALLY!  Someone else that dislikes the idea of a pointer to nothing ...
>>Can't we define a type called generic????  (You know, like a generic pointer).

>I'm afraid you missed the point.  If the only way to write reusable
>code turns out to be to use "generic" (or "void *") everywhere, what's
>the point of pretending to have a type checker?  People griped about
>this for Cedar Mesa and Modula-2+, but at least there they had
>run-time checking of type conversions from generic-to-specific.

Maybe I'm missing the point here too.  You still can have a strongly
typed language, as long as you carefully encapsulate all type-unsafe
casts into small classes where a reader easily can see that you don't
lie.  Example follows:

template<class T> class Stack_of_p : Stack<void*> {
public:
  void push(T* t) { Stack<void*>::push(t); }
  T* pop() { return (T*)Stack<void*>::pop(); }
  //...
};

It's easy to see that every Stack_of_p<T>::push(T*) implies
a cast from T* to void*, and thus the reverse cast in
Stack_of_p<T>::pop() is type-safe!  (In case the usual
stack semantics apply, of course...)

				Niklas

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