Perl 6中nativecast转为repr('CPointer')对象GC时是否触发DESTROY？

Great question—your hunch here is actually correct, and let me walk through why this works, plus how you could easily verify it yourself.

First, let's recap how repr('CPointer') classes interact with NativeCall and Perl 6's garbage collector:

• When NativeCall returns a pointer directly to an instance of a repr('CPointer') class, it sets up the instance to track the underlying C pointer's lifecycle. The key here is the representation type of the object, not how it was initially created.
• The DESTROY method on these classes is tied to the object's CPointer representation—Perl 6's GC checks the repr type when cleaning up objects, and triggers DESTROY for any CPointer-backed instances, regardless of how they were instantiated.

Now, for nativecast:

• nativecast(MyCPointerClass, $generic-pointer) doesn't just do a type cast—it creates a proper instance of MyCPointerClass that wraps the underlying C pointer. This instance has the same CPointer representation as if NativeCall had returned it directly.
• Once that wrapped instance is created, the GC treats it exactly like any other repr('CPointer') object. When the instance goes out of scope and is marked for collection, the DESTROY method will be called, letting you clean up the C memory as intended.

Quick Verification Trick #

To confirm this works in your code, add a debug print to your DESTROY method:

class MyCPointer is repr('CPointer') {
    method DESTROY() {
        say "DESTROY triggered for pointer: {self}";
        # Your C memory cleanup code here, e.g.:
        # native_lib::free(self);
    }
}

# Example usage
my Pointer $generic-ptr = native_lib::allocate_some_memory();
my MyCPointer $wrapped = nativecast(MyCPointer, $generic-ptr);

# Force the wrapped instance to be eligible for GC
$wrapped = Nil;
GC.collect; # Trigger garbage collection manually

If you see the "DESTROY triggered..." message in your output, that confirms the method is being called correctly.

In short: Your initial speculation holds up—nativecast-ed repr('CPointer') instances will have their DESTROY methods triggered during garbage collection, just like instances returned directly by NativeCall.

内容的提问来源于stack exchange，提问作者Curt Tilmes