Path: utzoo!attcan!uunet!pyrdc!pyrnj!rutgers!apple!scott
From: scott@Apple.COM (scott douglass)
Newsgroups: comp.lang.c++
Subject: Can you prohibit member functions from modifying *this?
Message-ID: <17192@apple.Apple.COM>
Date: 15 Sep 88 19:55:54 GMT
Reply-To: scott@apple.com (scott douglass)
Organization: Apple Computer, Inc.   Cupertion, CA
Lines: 60

If I have a class A and I have a const A* ap, should I be allowed to
invoke ap->f() which may modify *ap?

class A {
  private:
        int val;
  public:
        A() { val = 0; }
        void stab(int i) { val = i; }
	int get() { return val; }
};
 
main()
{
        A a;
        a.stab(4);              // this is fine

        const A* ap = &a;
        ap->stab(5);            // this is questionable

	const A ca;
	ca.stab(6);		// this is questionable, too
}

CFront allows all of these, effectively ignoring the const in the cases I
marked as questionable.  It would be useful to prohibit the questionable
cases above but instead be able to delcare a member function (such as get()
above) that had its implicit this argument declared as a const pointer.  I will
even be so bold as to propose an ugly, flawed syntax which I trust someone
can improve on (please):

class A {
  private:
        int val;
  public:
        A() { val = 0; }
        void stab(int i) { val = i; }
  const:
	int get() { return val; }
};
 
main()
{
        A a;
        a.stab(4);              // this is fine
	int i = a.get();	// this is fine, too

        const A* ap = &a;
        ap->stab(5);            // this is illegal
	i = ap->get();		// this is fine, too

	const A ca;
	ca.stab(6);		// this is illegal, too
	i = ca.get();		// this is fine, too
}
				--scott douglass
Any opinions above may be mine and are not necessarily those of Apple Computer.
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