Re: Potential strategy for avoiding problems with copy of a struct (maybe??)

[james.p.leblanc via Digitalmars-d-learn]

On Sunday, 22 August 2021 at 11:10:33 UTC, jfondren wrote:
On Sunday, 22 August 2021 at 07:58:12 UTC, james.p.leblanc 
wrote:
Hello,
If you don't get an answer that you like, I suggesting posting 
functional code and then stating your dissastisfactions with it.

Mattias, jfondren,

Thanks both for your replies, I always learn something from them.

I've trimmed my code to a minimal example to give a better idea
of my thinking on this.  You will notice that  to ensure that I
"seed" x with its real address at initialization, I must add 
@disable
this() to my struct.

import std.stdio;

    struct Foo {
        int a, b, c;
        Foo* myadd;

        this(int a, int b, int c) {
            this.a = a;
            this.b = b;
            this.c = c;
            this.myadd = &this;
        }

        @ disable this();
    }

    void main() {

        // x is original, we wish to protect
        auto x = Foo(1, 2, 3);

        // y is the "bad copy", do not want operation on y to 
pollute original x
        auto y=x;

        writeln("&x: ",&x,", x.myadd: ",x.myadd,", the 2 agree, 
we have original!");
        writeln("&y: ",&y,", y.myadd: ",y.myadd,", these 2 
disagree (must be a bad copy!");

}

Produces output:

&x: **7FFC65C02CC8**, x.myadd: **7FFC65C02CC8**, the 2 agree, we 
have original!
&y: 7FFC65C02CE8, y.myadd: **7FFC65C02CC8**, these 2 disagree 
(must be a bad copy!

So, as stated, in my struct overloading I can check if my two 
values agree
or not (exposing whether or not I have the original, or a copy), 
and react
appropriately.

I understand that the language allows circumvention of this 
method... but
I just want to catch minor mistakes in programming.

Again, all comments and thoughts are welcome.

Best Regards,
James