generic arenas

src/gc-arena/src/arena.rs

@@ -97,18 +97,14 @@ impl ArenaParameters {
 /// pointers and manually ensuring that invariants are held.
 #[macro_export]
 macro_rules! make_arena {
-    ($arena:ident, $root:ident) => {
-        make_arena!(pub(self) $arena, $root);
-    };
-
-    ($vis:vis $arena:ident, $root:ident) => {
+    ($vis:vis $arena:ident $(( $($arena_gen:tt)* ))?, $root:ident $(( $($root_gen:tt)* ))?) => {
         // Instead of generating an impl of `RootProvider`, we use a trait object.
         // The projection `<R as RootProvider<'gc>>::Root` is used to obtain the root
         // type with the lifetime `'gc` applied
         // By using a trait object, we avoid the need to generate a new type for each
         // invocation of this macro, which would lead to name conflicts if the macro was
         // used multiple times in the same scope.
-        $vis type $arena = $crate::Arena<dyn for<'a> $crate::RootProvider<'a, Root = $root<'a>>>;
+        $vis type $arena $( <$($arena_gen)*> )? = $crate::Arena<dyn for<'gc> $crate::RootProvider<'gc, Root = $root<'gc, $( $($root_gen)* )?>>>;
     };
 }
 

src/gc-arena/tests/tests.rs

@@ -251,6 +251,27 @@ fn derive_collect() {
     assert_eq!(Test8::needs_trace(), false);
 }
 
+#[test]
+fn generic_make_arena() {
+    #[derive(Collect)]
+    #[collect(no_drop)]
+    struct Test<'gc, T: 'gc + Collect, const N: usize, U: 'gc + Collect>(Gc<'gc, T>, [(); N], U);
+    make_arena!(TestArena(T, const N: usize, U), Test((T, T), N, Gc<'gc, U>));
+
+    fn test<const N: usize, T: 'static + Collect + Copy, U: 'static + Collect + Copy>(
+        v: T,
+        x: U,
+    ) -> ((T, T), usize, U) {
+        let arena = TestArena::<T, N, U>::new(Default::default(), |mc| {
+            Test(Gc::allocate(mc, (v, v)), [(); N], Gc::allocate(mc, x))
+        });
+        arena.mutate(|_, arena| (*arena.0, arena.1.len(), *arena.2))
+    }
+
+    assert_eq!(test::<12, _, _>(34, 12i8), ((34, 34), 12, 12i8));
+    assert_eq!(test::<7, _, _>(false, -6i64), ((false, false), 7, -6i64));
+}
+
 #[test]
 fn ui() {
     let t = trybuild::TestCases::new();