Fallout: add phantom data to the type inferencer

Author: nikomatsakis

src/librustc/middle/infer/type_variable.rs

@@ -14,6 +14,7 @@ use self::UndoEntry::*;
 
 use middle::ty::{self, Ty};
 use std::cmp::min;
+use std::marker::PhantomData;
 use std::mem;
 use std::u32;
 use util::snapshot_vec as sv;
@@ -42,7 +43,7 @@ enum UndoEntry {
     Relate(ty::TyVid, ty::TyVid),
 }
 
-struct Delegate<'tcx>;
+struct Delegate<'tcx>(PhantomData<&'tcx ()>);
 
 type Relation = (RelationDir, ty::TyVid);
 
@@ -64,7 +65,7 @@ impl RelationDir {
 
 impl<'tcx> TypeVariableTable<'tcx> {
     pub fn new() -> TypeVariableTable<'tcx> {
-        TypeVariableTable { values: sv::SnapshotVec::new(Delegate) }
+        TypeVariableTable { values: sv::SnapshotVec::new(Delegate(PhantomData)) }
     }
 
     fn relations<'a>(&'a mut self, a: ty::TyVid) -> &'a mut Vec<Relation> {

src/librustc/middle/infer/unify.rs

@@ -18,6 +18,7 @@ use middle::infer::{uok, ures};
 use middle::infer::InferCtxt;
 use std::cell::RefCell;
 use std::fmt::Debug;
+use std::marker::PhantomData;
 use syntax::ast;
 use util::snapshot_vec as sv;
 
@@ -79,7 +80,7 @@ pub struct UnificationTable<K:UnifyKey> {
 /// made during the snapshot may either be *committed* or *rolled back*.
 pub struct Snapshot<K:UnifyKey> {
     // Link snapshot to the key type `K` of the table.
-    marker: marker::CovariantType<K>,
+    marker: marker::PhantomData<K>,
     snapshot: sv::Snapshot,
 }
 
@@ -92,7 +93,7 @@ pub struct Node<K:UnifyKey> {
 }
 
 #[derive(Copy)]
-pub struct Delegate<K>;
+pub struct Delegate<K>(PhantomData<K>);
 
 // We can't use V:LatticeValue, much as I would like to,
 // because frequently the pattern is that V=Option<U> for some
@@ -102,14 +103,14 @@ pub struct Delegate<K>;
 impl<K:UnifyKey> UnificationTable<K> {
     pub fn new() -> UnificationTable<K> {
         UnificationTable {
-            values: sv::SnapshotVec::new(Delegate),
+            values: sv::SnapshotVec::new(Delegate(PhantomData)),
         }
     }
 
     /// Starts a new snapshot. Each snapshot must be either
     /// rolled back or committed in a "LIFO" (stack) order.
     pub fn snapshot(&mut self) -> Snapshot<K> {
-        Snapshot { marker: marker::CovariantType::<K>,
+        Snapshot { marker: marker::PhantomData::<K>,
                    snapshot: self.values.start_snapshot() }
     }