On 8/12/21 10:08 AM, Learner wrote:
On Thursday, 12 August 2021 at 13:56:17 UTC, Paul Backus wrote:
On Thursday, 12 August 2021 at 12:10:49 UTC, Learner wrote:
That worked fine, but the codebase is @safe:
```d
cast from `int[]` to `inout(int[])` not allowed in safe code
```
So copy constructors force me to introduce trusted methods, while
that was not necessary with postblits?
A postblit would simply ignore the type qualifier--which can lead to
undefined behavior. (Scroll down to the paragraph that begins "An
unqualified postblit..." under ["Struct Postblits"][1] in the spec.)
The copy constructor merely forces you to be honest about the safety
of your code.
In your case, I would recommend encapsulating the unsafe cast in a
function like the following:
```d
T[] dupWithQualifiers(T[] array)
{
auto copy = array.dup;
return (() @trusted => cast(T[]) copy)();
}
```
You can then use this function in place of `dup` in your copy
constructor.
[1]: https://dlang.org/spec/struct.html#struct-postblit
Thank you, now everything is more clear.
A last question, if you do not mind, just to better understand inout. It
seems a shortcut to avoid repeating the same function body for mutable,
const, and immutable. Why the following code is not equal to the single
inout constructor?
struct A {
int[] data;
//this(ref return scope inout A rhs) inout { /*body*/ }
this(ref return scope Timestamp rhs) { /*body*/ }
this(ref return scope const Timestamp rhs) const { /*body*/ }
this(ref return scope immutable Timestamp rhs) immutable {
/*body*/ }
}
Error: Generating an `inout` copy constructor for `struct B`
failed, therefore instances of it are uncopyable
Inout is compatible only with inout, and not with the unrolled code it
implies?
inout is not like a template. It's a separate qualifier that generates
only one function (not 3 unrolled ones).
It's sort of viral like const is viral -- all underlying pieces have to
support inout in order for you to write inout functions.
-Steve
