Implement variance RFC #738

src/doc/reference.md

@@ -576,7 +576,7 @@ the final namespace qualifier is omitted.
 Two examples of paths with type arguments:
 
 ```
-# struct HashMap<K, V>;
+# struct HashMap<K, V>(K,V);
 # fn f() {
 # fn id<T>(t: T) -> T { t }
 type T = HashMap<i32,String>; // Type arguments used in a type expression
@@ -1603,7 +1603,7 @@ pointer values (pointing to a type for which an implementation of the given
 trait is in scope) to pointers to the trait name, used as a type.
 
 ```
-# trait Shape { }
+# trait Shape { fn dummy(&self) { } }
 # impl Shape for i32 { }
 # let mycircle = 0i32;
 let myshape: Box<Shape> = Box::new(mycircle) as Box<Shape>;
@@ -1634,8 +1634,8 @@ let x: f64 = Num::from_i32(42);
 Traits may inherit from other traits. For example, in
 
 ```
-trait Shape { fn area() -> f64; }
-trait Circle : Shape { fn radius() -> f64; }
+trait Shape { fn area(&self) -> f64; }
+trait Circle : Shape { fn radius(&self) -> f64; }
 ```
 
 the syntax `Circle : Shape` means that types that implement `Circle` must also
@@ -1729,7 +1729,7 @@ type parameters taken by the trait it implements. Implementation parameters
 are written after the `impl` keyword.
 
 ```
-# trait Seq<T> { }
+# trait Seq<T> { fn dummy(&self, _: T) { } }
 impl<T> Seq<T> for Vec<T> {
    /* ... */
 }

src/libarena/lib.rs

@@ -96,7 +96,7 @@ pub struct Arena<'longer_than_self> {
     head: RefCell<Chunk>,
     copy_head: RefCell<Chunk>,
     chunks: RefCell<Vec<Chunk>>,
-    _invariant: marker::InvariantLifetime<'longer_than_self>,
+    _marker: marker::PhantomData<*mut &'longer_than_self()>,
 }
 
 impl<'a> Arena<'a> {
@@ -111,7 +111,7 @@ impl<'a> Arena<'a> {
             head: RefCell::new(chunk(initial_size, false)),
             copy_head: RefCell::new(chunk(initial_size, true)),
             chunks: RefCell::new(Vec::new()),
-            _invariant: marker::InvariantLifetime,
+            _marker: marker::PhantomData,
         }
     }
 }
@@ -361,6 +361,8 @@ pub struct TypedArena<T> {
 }
 
 struct TypedArenaChunk<T> {
+    marker: marker::PhantomData<T>,
+
     /// Pointer to the next arena segment.
     next: *mut TypedArenaChunk<T>,
 

src/libcollections/btree/map.rs

@@ -512,13 +512,22 @@ mod stack {
     use super::super::node::handle;
     use vec::Vec;
 
+    struct InvariantLifetime<'id>(
+        marker::PhantomData<::core::cell::Cell<&'id ()>>);
+
+    impl<'id> InvariantLifetime<'id> {
+        fn new() -> InvariantLifetime<'id> {
+            InvariantLifetime(marker::PhantomData)
+        }
+    }
+
     /// A generic mutable reference, identical to `&mut` except for the fact that its lifetime
     /// parameter is invariant. This means that wherever an `IdRef` is expected, only an `IdRef`
     /// with the exact requested lifetime can be used. This is in contrast to normal references,
     /// where `&'static` can be used in any function expecting any lifetime reference.
     pub struct IdRef<'id, T: 'id> {
         inner: &'id mut T,
-        marker: marker::InvariantLifetime<'id>
+        _marker: InvariantLifetime<'id>,
     }
 
     impl<'id, T> Deref for IdRef<'id, T> {
@@ -560,7 +569,7 @@ mod stack {
     pub struct Pusher<'id, 'a, K:'a, V:'a> {
         map: &'a mut BTreeMap<K, V>,
         stack: Stack<K, V>,
-        marker: marker::InvariantLifetime<'id>
+        _marker: InvariantLifetime<'id>,
     }
 
     impl<'a, K, V> PartialSearchStack<'a, K, V> {
@@ -595,11 +604,11 @@ mod stack {
             let pusher = Pusher {
                 map: self.map,
                 stack: self.stack,
-                marker: marker::InvariantLifetime
+                _marker: InvariantLifetime::new(),
             };
             let node = IdRef {
                 inner: unsafe { &mut *self.next },
-                marker: marker::InvariantLifetime
+                _marker: InvariantLifetime::new(),
             };
 
             closure(pusher, node)

src/libcollections/btree/node.rs

@@ -21,10 +21,11 @@ use core::prelude::*;
 use core::borrow::BorrowFrom;
 use core::cmp::Ordering::{Greater, Less, Equal};
 use core::iter::Zip;
+use core::marker::PhantomData;
 use core::ops::{Deref, DerefMut, Index, IndexMut};
 use core::ptr::Unique;
 use core::{slice, mem, ptr, cmp, num, raw};
-use alloc::heap;
+use alloc::heap::{self, EMPTY};
 
 /// Represents the result of an Insertion: either the item fit, or the node had to split
 pub enum InsertionResult<K, V> {
@@ -57,8 +58,8 @@ pub struct Node<K, V> {
     keys: Unique<K>,
     vals: Unique<V>,
 
-    // In leaf nodes, this will be null, and no space will be allocated for edges.
-    edges: Unique<Node<K, V>>,
+    // In leaf nodes, this will be None, and no space will be allocated for edges.
+    edges: Option<Unique<Node<K, V>>>,
 
     // At any given time, there will be `_len` keys, `_len` values, and (in an internal node)
     // `_len + 1` edges. In a leaf node, there will never be any edges.
@@ -278,8 +279,11 @@ impl<T> Drop for RawItems<T> {
 #[unsafe_destructor]
 impl<K, V> Drop for Node<K, V> {
     fn drop(&mut self) {
-        if self.keys.ptr.is_null() {
-            // We have already cleaned up this node.
+        if self.keys.is_null() {
+            // Since we have #[unsafe_no_drop_flag], we have to watch
+            // out for a null value being stored in self.keys. (Using
+            // null is technically a violation of the `Unique`
+            // requirements, though.)
             return;
         }
 
@@ -292,7 +296,7 @@ impl<K, V> Drop for Node<K, V> {
             self.destroy();
         }
 
-        self.keys.ptr = ptr::null_mut();
+        self.keys = unsafe { Unique::new(0 as *mut K) };
     }
 }
 
@@ -308,9 +312,9 @@ impl<K, V> Node<K, V> {
         let (vals_offset, edges_offset) = calculate_offsets_generic::<K, V>(capacity, false);
 
         Node {
-            keys: Unique(buffer as *mut K),
-            vals: Unique(buffer.offset(vals_offset as isize) as *mut V),
-            edges: Unique(buffer.offset(edges_offset as isize) as *mut Node<K, V>),
+            keys: Unique::new(buffer as *mut K),
+            vals: Unique::new(buffer.offset(vals_offset as isize) as *mut V),
+            edges: Some(Unique::new(buffer.offset(edges_offset as isize) as *mut Node<K, V>)),
             _len: 0,
             _capacity: capacity,
         }
@@ -326,9 +330,9 @@ impl<K, V> Node<K, V> {
         let (vals_offset, _) = calculate_offsets_generic::<K, V>(capacity, true);
 
         Node {
-            keys: Unique(buffer as *mut K),
-            vals: Unique(unsafe { buffer.offset(vals_offset as isize) as *mut V }),
-            edges: Unique(ptr::null_mut()),
+            keys: unsafe { Unique::new(buffer as *mut K) },
+            vals: unsafe { Unique::new(buffer.offset(vals_offset as isize) as *mut V) },
+            edges: None,
             _len: 0,
             _capacity: capacity,
         }
@@ -337,18 +341,18 @@ impl<K, V> Node<K, V> {
     unsafe fn destroy(&mut self) {
         let (alignment, size) =
                 calculate_allocation_generic::<K, V>(self.capacity(), self.is_leaf());
-        heap::deallocate(self.keys.ptr as *mut u8, size, alignment);
+        heap::deallocate(*self.keys as *mut u8, size, alignment);
     }
 
     #[inline]
     pub fn as_slices<'a>(&'a self) -> (&'a [K], &'a [V]) {
         unsafe {(
             mem::transmute(raw::Slice {
-                data: self.keys.ptr,
+                data: *self.keys as *const K,
                 len: self.len()
             }),
             mem::transmute(raw::Slice {
-                data: self.vals.ptr,
+                data: *self.vals as *const V,
                 len: self.len()
             })
         )}
@@ -367,8 +371,12 @@ impl<K, V> Node<K, V> {
             &[]
         } else {
             unsafe {
+                let data = match self.edges {
+                    None => heap::EMPTY as *const Node<K,V>,
+                    Some(ref p) => **p as *const Node<K,V>,
+                };
                 mem::transmute(raw::Slice {
-                    data: self.edges.ptr,
+                    data: data,
                     len: self.len() + 1
                 })
             }
@@ -524,7 +532,8 @@ impl<K: Clone, V: Clone> Clone for Node<K, V> {
 #[derive(Copy)]
 pub struct Handle<NodeRef, Type, NodeType> {
     node: NodeRef,
-    index: usize
+    index: usize,
+    marker: PhantomData<(Type, NodeType)>,
 }
 
 pub mod handle {
@@ -548,8 +557,8 @@ impl<K: Ord, V> Node<K, V> {
         // For the B configured as of this writing (B = 6), binary search was *significantly*
         // worse for usizes.
         match node.as_slices_internal().search_linear(key) {
-            (index, true) => Found(Handle { node: node, index: index }),
-            (index, false) => GoDown(Handle { node: node, index: index }),
+            (index, true) => Found(Handle { node: node, index: index, marker: PhantomData }),
+            (index, false) => GoDown(Handle { node: node, index: index, marker: PhantomData }),
         }
     }
 }
@@ -586,7 +595,7 @@ impl <K, V> Node<K, V> {
 
     /// If the node has any children
     pub fn is_leaf(&self) -> bool {
-        self.edges.ptr.is_null()
+        self.edges.is_none()
     }
 
     /// if the node has too few elements
@@ -618,7 +627,8 @@ impl<K, V, NodeRef, Type, NodeType> Handle<NodeRef, Type, NodeType> where
     pub fn as_raw(&mut self) -> Handle<*mut Node<K, V>, Type, NodeType> {
         Handle {
             node: &mut *self.node as *mut _,
-            index: self.index
+            index: self.index,
+            marker: PhantomData,
         }
     }
 }
@@ -630,7 +640,8 @@ impl<K, V, Type, NodeType> Handle<*mut Node<K, V>, Type, NodeType> {
     pub unsafe fn from_raw<'a>(&'a self) -> Handle<&'a Node<K, V>, Type, NodeType> {
         Handle {
             node: &*self.node,
-            index: self.index
+            index: self.index,
+            marker: PhantomData,
         }
     }
 
@@ -640,7 +651,8 @@ impl<K, V, Type, NodeType> Handle<*mut Node<K, V>, Type, NodeType> {
     pub unsafe fn from_raw_mut<'a>(&'a mut self) -> Handle<&'a mut Node<K, V>, Type, NodeType> {
         Handle {
             node: &mut *self.node,
-            index: self.index
+            index: self.index,
+            marker: PhantomData,
         }
     }
 }
@@ -688,12 +700,14 @@ impl<K, V, NodeRef: Deref<Target=Node<K, V>>, Type> Handle<NodeRef, Type, handle
         if self.node.is_leaf() {
             Leaf(Handle {
                 node: self.node,
-                index: self.index
+                index: self.index,
+                marker: PhantomData,
             })
         } else {
             Internal(Handle {
                 node: self.node,
-                index: self.index
+                index: self.index,
+                marker: PhantomData,
             })
         }
     }
@@ -826,7 +840,8 @@ impl<K, V, NodeRef, NodeType> Handle<NodeRef, handle::Edge, NodeType> where
     unsafe fn left_kv<'a>(&'a mut self) -> Handle<&'a mut Node<K, V>, handle::KV, NodeType> {
         Handle {
             node: &mut *self.node,
-            index: self.index - 1
+            index: self.index - 1,
+            marker: PhantomData,
         }
     }
 
@@ -836,7 +851,8 @@ impl<K, V, NodeRef, NodeType> Handle<NodeRef, handle::Edge, NodeType> where
     unsafe fn right_kv<'a>(&'a mut self) -> Handle<&'a mut Node<K, V>, handle::KV, NodeType> {
         Handle {
             node: &mut *self.node,
-            index: self.index
+            index: self.index,
+            marker: PhantomData,
         }
     }
 }
@@ -876,7 +892,8 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<&'a mut Node<K, V>, handle::KV, NodeType
     pub fn into_left_edge(self) -> Handle<&'a mut Node<K, V>, handle::Edge, NodeType> {
         Handle {
             node: &mut *self.node,
-            index: self.index
+            index: self.index,
+            marker: PhantomData,
         }
     }
 }
@@ -926,7 +943,8 @@ impl<K, V, NodeRef, NodeType> Handle<NodeRef, handle::KV, NodeType> where
     pub fn left_edge<'a>(&'a mut self) -> Handle<&'a mut Node<K, V>, handle::Edge, NodeType> {
         Handle {
             node: &mut *self.node,
-            index: self.index
+            index: self.index,
+            marker: PhantomData,
         }
     }
 
@@ -935,7 +953,8 @@ impl<K, V, NodeRef, NodeType> Handle<NodeRef, handle::KV, NodeType> where
     pub fn right_edge<'a>(&'a mut self) -> Handle<&'a mut Node<K, V>, handle::Edge, NodeType> {
         Handle {
             node: &mut *self.node,
-            index: self.index + 1
+            index: self.index + 1,
+            marker: PhantomData,
         }
     }
 }
@@ -1044,7 +1063,8 @@ impl<K, V> Node<K, V> {
         debug_assert!(index < self.len(), "kv_handle index out of bounds");
         Handle {
             node: self,
-            index: index
+            index: index,
+            marker: PhantomData,
         }
     }
 
@@ -1064,7 +1084,7 @@ impl<K, V> Node<K, V> {
                     vals: RawItems::from_slice(self.vals()),
                     edges: RawItems::from_slice(self.edges()),
 
-                    ptr: self.keys.ptr as *mut u8,
+                    ptr: *self.keys as *mut u8,
                     capacity: self.capacity(),
                     is_leaf: self.is_leaf()
                 },