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From: connolly@livy.cs.umass.edu (Christopher Connolly)
Newsgroups: comp.lang.c++,comp.lang.objective-c
Subject: Re: Static typing, OOP efficiency, and programmer error
Message-ID: <28148@dime.cs.umass.edu>
Date: 19 Mar 91 20:23:04 GMT
References: <27CE9C05.4F64@tct.uucp> <1860@news.tcs.com> <47199@nigel.ee.udel.edu> <27E17FD1.7241@tct.uucp>
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Reply-To: connolly@livy.cs.umass.edu (Christopher Ian Connolly)
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Organization: University of Massachusetts, Amherst
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In article <27E17FD1.7241@tct.uucp> chip@tct.uucp (Chip Salzenberg) writes:
>According to carroll@cis.udel.edu (Mark Carroll):
>>... by using dataflow analysis to bind statically whenever possible,
>>any of the errors that could be caught statically in C++ could be caught
>>statically in Objective-C.
>
>I think that the above statement is incorrect.  The C++ language is
>incapable of compiling a program that results in an object receiving a
>message it can't handle.

I don't know much about Objective-C, so I can't say anything about
Mark Carroll's statement.  On the other hand, the AT&T version 2.1 C++
translator will successfully compile this program:
/////////////////////////////////////////////////////////////////////
#include <stream.h>

struct junk
{
  int foo;
  virtual int barf() { cout << "Bandaged Knuckles.\n" << flush; return(foo); }
};

struct eat_me { int foo; };

main()
{
  junk* fool_me_once;
  eat_me* fool_me_twice;
  void* bar;

  cout << "Let the festivities begin.\n";

  fool_me_once = new junk;
  fool_me_once->foo = 1;
  fool_me_once->barf();

  fool_me_twice = new eat_me;
  fool_me_twice->foo = 2;

  bar = (void*) fool_me_twice;

  fool_me_once = (junk*) bar;
  fool_me_once->barf();
}
/////////////////////////////////////////////////////////////////////
The resulting executable (a.out) prints this:

sunbeam% a.out
Let the festivities begin.
Bandaged Knuckles.
Segmentation fault (core dumped)
sunbeam%

This is a case where an object is "receiving a message it can't
handle", the result being a segmentation fault.  Nicht wahr?

>I am not willing to sacrifice type safety for elegance.

I'd like both, with an order of magnitude to go, please.

		-C. Connolly