From 54d88f88c6bbc001ff84902c2b03d9db01d91dee Mon Sep 17 00:00:00 2001
From: Troy Hinckley <t.macman@gmail.com>
Date: Fri, 22 Dec 2023 12:27:22 -0600
Subject: [PATCH] Implement `Rt<[T; N]>`

This will remove even more allocations from function calls
---
 src/core/gc/root.rs  | 46 ++++++++++++++++++++++++++++++++++++++++----
 src/core/gc/trace.rs |  8 ++++++++
 src/fns.rs           | 20 ++++++++-----------
 src/interpreter.rs   |  8 +++-----
 4 files changed, 61 insertions(+), 21 deletions(-)

diff --git a/src/core/gc/root.rs b/src/core/gc/root.rs
index 18cb912a..3333e579 100644
--- a/src/core/gc/root.rs
+++ b/src/core/gc/root.rs
@@ -212,6 +212,20 @@ where
     }
 }
 
+impl<'new, T, const N: usize> WithLifetime<'new> for [T; N]
+where
+    T: WithLifetime<'new>,
+{
+    type Out = [<T as WithLifetime<'new>>::Out; N];
+    unsafe fn with_lifetime(self) -> Self::Out {
+        // work around since we can't transmute arrays
+        let ptr = &self as *const [T; N] as *const Self::Out;
+        let value = unsafe { ptr.read() };
+        std::mem::forget(self);
+        value
+    }
+}
+
 impl<'new, T> WithLifetime<'new> for Vec<T>
 where
     T: WithLifetime<'new>,
@@ -445,6 +459,34 @@ impl<T> Rt<Option<T>> {
     }
 }
 
+impl<T, I, const N: usize> Index<I> for Rt<[T; N]>
+where
+    [Rt<T>]: Index<I>,
+{
+    type Output = <[Rt<T>] as Index<I>>::Output;
+
+    fn index(&self, index: I) -> &Self::Output {
+        let slice = unsafe { std::mem::transmute::<&[T], &[Rt<T>]>(&self.inner) };
+        Index::index(slice, index)
+    }
+}
+
+impl<T, I, const N: usize> IndexMut<I> for Rt<[T; N]>
+where
+    [Rt<T>]: IndexMut<I>,
+{
+    fn index_mut(&mut self, index: I) -> &mut Self::Output {
+        let slice = unsafe { std::mem::transmute::<&mut [T], &mut [Rt<T>]>(&mut self.inner) };
+        IndexMut::index_mut(slice, index)
+    }
+}
+
+impl<T, const N: usize> AsRef<[Rt<T>]> for Rt<[T; N]> {
+    fn as_ref(&self) -> &[Rt<T>] {
+        unsafe { std::mem::transmute::<&[T], &[Rt<T>]>(&self.inner) }
+    }
+}
+
 impl<T> Rt<Vec<T>> {
     // This is not safe to expose pub(crate) because you could call pop and get
     // an owned Rt
@@ -465,10 +507,6 @@ impl<T> Rt<Vec<T>> {
         self.as_mut_ref().pop();
     }
 
-    pub(crate) fn clear(&mut self) {
-        self.as_mut_ref().clear();
-    }
-
     pub(crate) fn swap_remove(&mut self, index: usize) {
         self.as_mut_ref().swap_remove(index);
     }
diff --git a/src/core/gc/trace.rs b/src/core/gc/trace.rs
index 5fba2bed..4a60b3ec 100755
--- a/src/core/gc/trace.rs
+++ b/src/core/gc/trace.rs
@@ -38,6 +38,14 @@ impl<T: Trace> Trace for [T] {
     }
 }
 
+impl<T: Trace, const N: usize> Trace for [T; N] {
+    fn trace(&self, stack: &mut Vec<RawObj>) {
+        for x in self {
+            x.trace(stack);
+        }
+    }
+}
+
 impl<T: Trace> Trace for Vec<T> {
     fn trace(&self, stack: &mut Vec<RawObj>) {
         for x in self {
diff --git a/src/fns.rs b/src/fns.rs
index 016454fe..76a588c0 100644
--- a/src/fns.rs
+++ b/src/fns.rs
@@ -436,18 +436,16 @@ fn sort<'ob>(
 
     root!(tmp, nil(), cx);
     root!(vec, cx);
-    // TODO: Use an array
-    root!(args, Vec::new(), cx);
+    root!(args, [nil(), nil()], cx);
     // A simple insertion sort
     // TODO: use a better sort like tim sort
     for i in 1..len {
         tmp.set(&vec[i]);
         let mut j = i;
         while j > 0 {
-            args.clear();
-            args.push(&vec[j - 1]);
-            args.push(&*tmp);
-            match predicate.call(args, None, env, cx) {
+            args[0].set(&vec[j - 1]);
+            args[1].set(&*tmp);
+            match predicate.call(&args[..], None, env, cx) {
                 Ok(cmp) => {
                     if cmp != nil() {
                         break;
@@ -690,21 +688,19 @@ fn maphash(
         }
     };
 
-    // TODO: Use array
-    root!(args, Vec::new(), cx);
+    root!(args, [nil(), nil()], cx);
     loop {
         {
             let mut view = table.bind(cx).untag().try_borrow_mut()?;
             let Some(idx) = get_idx(&mut view) else { break };
             let (key, val) = view.get_index(idx).unwrap();
-            args.push(*key);
-            args.push(*val);
+            args[0].set(*key);
+            args[1].set(*val);
         }
-        if let Err(e) = function.call(args, None, env, cx) {
+        if let Err(e) = function.call(&args[..], None, env, cx) {
             table.bind(cx).untag().try_borrow_mut().unwrap().iter_next = 0;
             return Err(e.into());
         }
-        args.clear();
     }
     table.bind(cx).untag().try_borrow_mut().unwrap().iter_next = 0;
     Ok(false)
diff --git a/src/interpreter.rs b/src/interpreter.rs
index 4d23dfb6..678252b4 100755
--- a/src/interpreter.rs
+++ b/src/interpreter.rs
@@ -215,11 +215,9 @@ impl Interpreter<'_, '_> {
                 let closure_fn: Result<&Rt<Gc<Function>>, _> = closure_fn.try_into();
                 if let Ok(closure_fn) = closure_fn {
                     root!(closure_fn, cx);
-                    // TODO: use array
-                    root!(args, Vec::new(), cx);
-                    args.push(form.bind(cx));
-                    args.push(env);
-                    return closure_fn.call(args, None, self.env, cx);
+                    let args = [form.bind(cx), env];
+                    root!(args, cx);
+                    return closure_fn.call(&args[..], None, self.env, cx);
                 }
             }
         }