On Saturday, 9 April 2022 at 10:39:33 UTC, vit wrote:
Why doesn't this code compile?
`proxySwap1` is lying about its attributes. It says `rhs` is
`scope`, but it escapes by assignment `this.ptr = rhs.ptr;`. The
compiler doesn't raise an error because it's marked `@trusted`.
`proxySwap2` is simply a template function wrapping `proxySwap1`,
attributes are inferred based on the signature you specified for
`proxySwap1` (even if it's wrong).
`proxySwap3` is a template function, so the compiler infers `rhs`
to be `return scope`. While a `@trusted` function allows you to
escape `scope` variables, the compiler will still try to infer
`scope`, `return scope` or `return ref` on its parameters as far
as it can, and that can spawn errors in its `@safe` callers.
Swapping `scope` variables is not something you can do in `@safe`
code with dip1000's current design, because of this:
```D
void main() @safe {
scope Foo a;
{
int x;
scope Foo b = Foo(&x);
a.proxySwap3(b); // scope variable `b` assigned to `a` with
longer lifetime
}
// a is now a dangling pointer
}
```
