fix paper example to use arena

ghostcell/examples/dlist_arc_paper.rs → ghostcell/examples/dlist_arena_paper.rs

-use ghostcell::dlist_arc::*;
+use ghostcell::dlist_arena::*;
+use typed_arena::Arena as TypedArena;
 use ghostcell::GhostToken;
 use std::sync::RwLock;
 use std::{fmt, thread, time};
 
-fn print_list<'id, T: fmt::Debug>(tag: char, list: &NodePtr<'id, T>, token: &GhostToken<'id>) {
+fn print_list<'arena, 'id, T: fmt::Debug>(tag: char, list: NodeRef<'arena, 'id, T>, token: &GhostToken<'id>) {
     for d in Node::iter(list, token) {
         print!("{}{:?}, ", tag, d);
     }
 }
 
-fn init_list<'id>(token: &mut GhostToken<'id>, list_size: u32) -> NodePtr<'id, u32> {
-    let head: NodePtr<u32> = Node::new(0);
-    let mut tail = Some(head.clone());
+fn init_list<'arena, 'id>(
+    arena: &'arena TypedArena<Node<'arena, 'id, u32>>,
+    token: &mut GhostToken<'id>,
+    list_size: u32
+) -> NodeRef<'arena, 'id, u32> {
+    let head: NodeRef<_> = Node::new(0, arena);
+    let mut tail = head;
 
     // To append to the list, we need a &mut GhostToken
     for i in 1..list_size {
-        let node = Node::new(i);
-        Node::insert_next(tail.take().unwrap(), &node, token);
-        tail = Some(node);
+        let node = Node::new(i, arena);
+        Node::insert_next(tail, node, token);
+        tail = node;
     }
 
     head
@@ -26,7 +31,8 @@ fn init_list<'id>(token: &mut GhostToken<'id>, list_size: u32) -> NodePtr<'id, u
 fn main() {
     GhostToken::new(|mut token| {
         // Allocate a list of size 50.
-        let list = init_list(&mut token, 50);
+        let arena = TypedArena::with_capacity(50);
+        let list = init_list(&arena, &mut token, 50);
 
         rayon::join(
             || Node::iterate(&list, &token, |n| print!("{:?}, ", n)),