Path: utzoo!mnetor!uunet!nbires!ncar!oddjob!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c++
Subject: Re: access functions
Message-ID: <11187@mimsy.UUCP>
Date: 23 Apr 88 06:21:30 GMT
References: <8063@apple.Apple.Com> <6590039@hplsla.HP.COM> <11152@mimsy.UUCP> <1490@pt.cs.cmu.edu>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 52

>In article <11152@mimsy.UUCP> I wrote the following key line
(but probably did not highlight it sufficiently):
>>The point, however, is that a variable is always
>>a variable, while a function is arbitrary.

In article <1490@pt.cs.cmu.edu> lindsay@K.GP.CS.CMU.EDU (Donald Lindsay)
writes:
>The functional approach has other virtues.

[various virtues deleted]

Agreed.  jima has a point, however: perhaps one should declare that
*all* object variables shall be retrieved through access functions,
but that argument-free functions should look like variables.  This
leaves one with the question of how to implement assignments to these.

One possible syntax:

	class c {
		int	var0;
		int	nv0;	// counts var0 refs
	public:
		int	var1;	// freely accessible

		/*
		 * Define access (read & write) functions for var0 that
		 * make it act like var1 without actually being the same
		 * as var1, and incidentally count references too.  If
		 * we defined only a read function, or only a write function,
		 * var1 would be a read-only or write-only variable.
		 */
		inline int var0() { this->nv0++; return this->var0; }
			// I never did like implicit references :-)
		inline int var0=(x) { this->nv0++; return this->var0 = x; }
			// Here the type of x is implicitly int.
			// x is any identifier, but there may be only one.

		c() { var0=0; nv0=0; var1=0; }
			// `local color' :-)
	};

Note that cfront already gives a `sorry, not implemented' error
for declarations of the form

	class c {
		int v;
	public:
		int v() { return this->v; }
	};
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris