On Tuesday, 1 March 2022 at 04:59:49 UTC, Mike Parker wrote:
On Tuesday, 1 March 2022 at 04:29:56 UTC, cc wrote:
```d
struct A {}
class B {
A opCast(T : A)() {
return A();
}
}
void main() {
auto b = new B();
destroy(b);
}
```
fails with
```
dmd2\windows\bin\..\..\src\druntime\import\object.d(4209):
Error: template instance `opCast!(void*)` does not match
template declaration `opCast(T : A)()`
main.d(9): Error: template instance `object.destroy!(true, B)`
error instantiating
```
Looks like a similar bug has been reported:
https://issues.dlang.org/show_bug.cgi?id=22635
Is it a bug? It's not documented in the `opCast` documentation,
but it looks like when you define an `opCast` it completely
replaces the default behavior, i.e., whatever type you define
as the target type becomes the only type to which you can
attempt to cast.
It's a bug in druntime. `destroy` needs to reinterpret the class
reference as a `void*` to pass it to `rt_finalize`:
https://github.com/dlang/druntime/blob/v2.098.1/src/object.d#L4209
However, `cast(void*)` is not the correct way to do this, because
it fails in the presence of `opCast`.
