On Sunday, 22 August 2021 at 13:03:20 UTC, james.p.leblanc wrote:
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.
I still really don't get what you're trying to do, to the point
of wanting to know: are you making 'myadd' a field for this
struct only so that you can check it against the address of the
variable? Or is it a real example of data you want to protect
from accidental copies that just, coincidentally, can also be
used to check if the struct has been copied? And, still, are you
sure that you want a struct and not a class?
The idea of not polluting the original of a struct requires some
reference types as members of the struct, or a pointer, as
otherwise everything is copied and the original is perfectly
'protected' anyway.
Here's a struct that
1. has an int* as an example of data that shouldn't be copied,
for example because it would result in a double free on
destruction
2. protects against bad copies, not by forbidding copies, but by
nulling the int* with a postblit
3. can then report that it's an original vs. a copy by seeing if
the int* is null
```d
import std.stdio;
import core.memory : pureMalloc, pureFree;
struct Foo {
int a, b, c;
int* unique;
this(int a, int b, int c) {
this.a = a;
this.b = b;
this.c = c;
unique = cast(int*) pureMalloc(int.sizeof);
*unique = a * b * c;
}
void report() const {
if (unique)
writeln("I'm the original: ", *unique);
else
writeln("I am an incomplete copy :(");
}
this(this) {
unique = null;
}
~this() {
pureFree(unique);
}
}
void alwaysGetsACopy(Foo f) {
assert(f.unique is null);
}
void reportIfOriginal(ref Foo f) {
if (f.unique !is null)
f.report;
}
void main() {
auto x = Foo(1, 2, 3);
auto y = x;
x.report; // I'm an original
y.report; // I'm a copy
x.alwaysGetsACopy; // assertion succeeds
x.reportIfOriginal; // I'm an original
y.reportIfOriginal;
}
```
