Refactor

src/lib.rs

@@ -84,12 +84,21 @@ impl Allocator {
         unsafe { GC_gcollect() }
     }
 
-    pub unsafe fn register_finalizer(
+    pub unsafe fn register_finalizer<F: FnOnce(*mut c_void) + 'static>(
         ptr: *const c_void,
-        finalizer: extern "C" fn(*mut c_void, *mut c_void),
+        finalizer: F,
-        client_data: *const c_void,
     ) {
-        GC_register_finalizer(ptr, finalizer, client_data, null(), null());
+        extern "C" fn finalize<F: FnOnce(*mut c_void)>(ptr: *mut c_void, data: *mut c_void) {
+            (unsafe { Box::from_raw(data as *mut F) })(ptr)
+        }
+
+        GC_register_finalizer(
+            ptr,
+            finalize::<F>,
+            Box::into_raw(Box::new(finalizer)) as *const _,
+            null(),
+            null(),
+        );
     }
 }