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From: budd@fog.CS.ORST.EDU (Tim Budd)
Newsgroups: comp.lang.c++
Subject: Re: Read-only data access
Message-ID: <1991Jun13.211926.20276@lynx.CS.ORST.EDU>
Date: 13 Jun 91 21:19:26 GMT
References: <1654@balrog.ctron.com>
Sender: @lynx.CS.ORST.EDU
Organization: Computer Science Department, Oregon State Univ.
Lines: 49
Nntp-Posting-Host: fog.cs.orst.edu

In article <1654@balrog.ctron.com> bangrazi@ctron.com writes:
>
>****************************
>
>class Z {
>public:
>    const int& z = &zP;
>private:
>    int zP;
>}
>
>int main ()
>{
>    Z* myZ = new Z;
>    printf ("%d\n", myZ.z);
>    delete myZ;
>}
>
>****************************
>

This is a neat trick.  I like it.  But I think some of the details are
wrong (at least they don't work as planned using GNU 1.37).  The declaration
needs to be int& const (reference to a constant), not const int & (constant
reference).  Also G++ doesn't like the constant assignment as shown, but
will allow me to put it in the constructor.

Here is the example fixed up (at least it works on MY machine).

class Z {
public:
	int& const z;
	Z() : z(zP) { zP = 12; }

	modifier() { /* methods can modify zP */ zP += 7; }
private:
	int zP;
};

int main ()
{
	Z* myZ = new Z;
	printf("%d\n", myZ->z);

	myZ->modifier();
	// myZ->z = 24; will generate an error

	printf("%d\n", myZ->z);
}