core: Remove the cast module

This commit revisits the `cast` module in libcore and libstd, and scrutinizes
all functions inside of it. The result was to remove the `cast` module entirely,
folding all functionality into the `mem` module. Specifically, this is the fate
of each function in the `cast` module.

* transmute - This function was moved to `mem`, but it is now marked as
              #[unstable]. This is due to planned changes to the `transmute`
              function and how it can be invoked (see the #[unstable] comment).
              For more information, see RFC 5 and #12898

* transmute_copy - This function was moved to `mem`, with clarification that is
                   is not an error to invoke it with T/U that are different
                   sizes, but rather that it is strongly discouraged. This
                   function is now #[stable]

* forget - This function was moved to `mem` and marked #[stable]

* bump_box_refcount - This function was removed due to the deprecation of
                      managed boxes as well as its questionable utility.

* transmute_mut - This function was previously deprecated, and removed as part
                  of this commit.

* transmute_mut_unsafe - This function doesn't serve much of a purpose when it
                         can be achieved with an `as` in safe code, so it was
                         removed.

* transmute_lifetime - This function was removed because it is likely a strong
                       indication that code is incorrect in the first place.

* transmute_mut_lifetime - This function was removed for the same reasons as
                           `transmute_lifetime`

* copy_lifetime - This function was moved to `mem`, but it is marked
                  `#[unstable]` now due to the likelihood of being removed in
                  the future if it is found to not be very useful.

* copy_mut_lifetime - This function was also moved to `mem`, but had the same
                      treatment as `copy_lifetime`.

* copy_lifetime_vec - This function was removed because it is not used today,
                      and its existence is not necessary with DST
                      (copy_lifetime will suffice).

In summary, the cast module was stripped down to these functions, and then the
functions were moved to the `mem` module.

    transmute - #[unstable]
    transmute_copy - #[stable]
    forget - #[stable]
    copy_lifetime - #[unstable]
    copy_mut_lifetime - #[unstable]

[breaking-change]

src/doc/guide-unsafe.md

@@ -66,11 +66,11 @@ restrictions is undefined behaviour. For example, the following
 creates two aliasing `&mut` pointers, and is invalid.
 
 ```
-use std::cast;
+use std::mem;
 let mut x: u8 = 1;
 
 let ref_1: &mut u8 = &mut x;
-let ref_2: &mut u8 = unsafe { cast::transmute_mut_lifetime(ref_1) };
+let ref_2: &mut u8 = unsafe { mem::transmute(&mut *ref_1) };
 
 // oops, ref_1 and ref_2 point to the same piece of data (x) and are
 // both usable

src/libarena/lib.rs

@@ -26,8 +26,6 @@
 
 extern crate collections;
 
-use std::cast::{transmute, transmute_mut_lifetime};
-use std::cast;
 use std::cell::{Cell, RefCell};
 use std::cmp;
 use std::intrinsics::{TyDesc, get_tydesc};
@@ -137,7 +135,7 @@ unsafe fn destroy_chunk(chunk: &Chunk) {
     let fill = chunk.fill.get();
 
     while idx < fill {
-        let tydesc_data: *uint = transmute(buf.offset(idx as int));
+        let tydesc_data: *uint = mem::transmute(buf.offset(idx as int));
         let (tydesc, is_done) = un_bitpack_tydesc_ptr(*tydesc_data);
         let (size, align) = ((*tydesc).size, (*tydesc).align);
 
@@ -187,28 +185,27 @@ impl Arena {
     #[inline]
     fn alloc_copy_inner(&mut self, n_bytes: uint, align: uint) -> *u8 {
         unsafe {
-            let this = transmute_mut_lifetime(self);
-            let start = round_up(this.copy_head.fill.get(), align);
+            let start = round_up(self.copy_head.fill.get(), align);
             let end = start + n_bytes;
             if end > self.chunk_size() {
-                return this.alloc_copy_grow(n_bytes, align);
+                return self.alloc_copy_grow(n_bytes, align);
             }
-            this.copy_head.fill.set(end);
+            self.copy_head.fill.set(end);
 
             //debug!("idx = {}, size = {}, align = {}, fill = {}",
             //       start, n_bytes, align, head.fill.get());
 
-            this.copy_head.as_ptr().offset(start as int)
+            self.copy_head.as_ptr().offset(start as int)
         }
     }
 
     #[inline]
     fn alloc_copy<'a, T>(&'a mut self, op: || -> T) -> &'a T {
         unsafe {
             let ptr = self.alloc_copy_inner(mem::size_of::<T>(), min_align_of::<T>());
-            let ptr: *mut T = transmute(ptr);
+            let ptr = ptr as *mut T;
             mem::move_val_init(&mut (*ptr), op());
-            return transmute(ptr);
+            return &*ptr;
         }
     }
 
@@ -228,26 +225,16 @@ impl Arena {
     fn alloc_noncopy_inner(&mut self, n_bytes: uint, align: uint)
                           -> (*u8, *u8) {
         unsafe {
-            let start;
-            let end;
-            let tydesc_start;
-            let after_tydesc;
-
-            {
-                let head = transmute_mut_lifetime(&mut self.head);
-
-                tydesc_start = head.fill.get();
-                after_tydesc = head.fill.get() + mem::size_of::<*TyDesc>();
-                start = round_up(after_tydesc, align);
-                end = start + n_bytes;
-            }
+            let tydesc_start = self.head.fill.get();
+            let after_tydesc = self.head.fill.get() + mem::size_of::<*TyDesc>();
+            let start = round_up(after_tydesc, align);
+            let end = start + n_bytes;
 
             if end > self.head.capacity() {
                 return self.alloc_noncopy_grow(n_bytes, align);
             }
 
-            let head = transmute_mut_lifetime(&mut self.head);
-            head.fill.set(round_up(end, mem::pref_align_of::<*TyDesc>()));
+            self.head.fill.set(round_up(end, mem::pref_align_of::<*TyDesc>()));
 
             //debug!("idx = {}, size = {}, align = {}, fill = {}",
             //       start, n_bytes, align, head.fill);
@@ -263,18 +250,18 @@ impl Arena {
             let tydesc = get_tydesc::<T>();
             let (ty_ptr, ptr) =
                 self.alloc_noncopy_inner(mem::size_of::<T>(), min_align_of::<T>());
-            let ty_ptr: *mut uint = transmute(ty_ptr);
-            let ptr: *mut T = transmute(ptr);
+            let ty_ptr = ty_ptr as *mut uint;
+            let ptr = ptr as *mut T;
             // Write in our tydesc along with a bit indicating that it
             // has *not* been initialized yet.
-            *ty_ptr = transmute(tydesc);
+            *ty_ptr = mem::transmute(tydesc);
             // Actually initialize it
             mem::move_val_init(&mut(*ptr), op());
             // Now that we are done, update the tydesc to indicate that
             // the object is there.
             *ty_ptr = bitpack_tydesc_ptr(tydesc, true);
 
-            return transmute(ptr);
+            return &*ptr;
         }
     }
 
@@ -283,7 +270,7 @@ impl Arena {
     pub fn alloc<'a, T>(&'a self, op: || -> T) -> &'a T {
         unsafe {
             // FIXME #13933: Remove/justify all `&T` to `&mut T` transmutes
-            let this: &mut Arena = transmute::<&_, &mut _>(self);
+            let this: &mut Arena = mem::transmute::<&_, &mut _>(self);
             if intrinsics::needs_drop::<T>() {
                 this.alloc_noncopy(op)
             } else {
@@ -366,7 +353,7 @@ impl<T> TypedArenaChunk<T> {
 
         let mut chunk = unsafe {
             let chunk = exchange_malloc(size);
-            let mut chunk: Box<TypedArenaChunk<T>> = cast::transmute(chunk);
+            let mut chunk: Box<TypedArenaChunk<T>> = mem::transmute(chunk);
             mem::move_val_init(&mut chunk.next, next);
             chunk
         };
@@ -387,7 +374,7 @@ impl<T> TypedArenaChunk<T> {
 
         let mut chunk = unsafe {
             let chunk = exchange_malloc(size, min_align_of::<TypedArenaChunk<T>>());
-            let mut chunk: Box<TypedArenaChunk<T>> = cast::transmute(chunk);
+            let mut chunk: Box<TypedArenaChunk<T>> = mem::transmute(chunk);
             mem::move_val_init(&mut chunk.next, next);
             chunk
         };
@@ -425,7 +412,7 @@ impl<T> TypedArenaChunk<T> {
     fn start(&self) -> *u8 {
         let this: *TypedArenaChunk<T> = self;
         unsafe {
-            cast::transmute(round_up(this.offset(1) as uint, min_align_of::<T>()))
+            mem::transmute(round_up(this.offset(1) as uint, min_align_of::<T>()))
         }
     }
 
@@ -463,12 +450,12 @@ impl<T> TypedArena<T> {
     pub fn alloc<'a>(&'a self, object: T) -> &'a T {
         unsafe {
             // FIXME #13933: Remove/justify all `&T` to `&mut T` transmutes
-            let this: &mut TypedArena<T> = cast::transmute::<&_, &mut _>(self);
+            let this: &mut TypedArena<T> = mem::transmute::<&_, &mut _>(self);
             if this.ptr == this.end {
                 this.grow()
             }
 
-            let ptr: &'a mut T = cast::transmute(this.ptr);
+            let ptr: &'a mut T = mem::transmute(this.ptr);
             mem::move_val_init(ptr, object);
             this.ptr = this.ptr.offset(1);
             let ptr: &'a T = ptr;

src/libcollections/dlist.rs

@@ -21,10 +21,9 @@
 // Backlinks over DList::prev are raw pointers that form a full chain in
 // the reverse direction.
 
-use std::cast;
 use std::iter::Rev;
 use std::iter;
-use std::mem::{replace, swap};
+use std::mem;
 use std::ptr;
 
 use deque::Deque;
@@ -93,13 +92,13 @@ impl<T> Rawlink<T> {
         if self.p.is_null() {
             None
         } else {
-            Some(unsafe { cast::transmute(self.p) })
+            Some(unsafe { mem::transmute(self.p) })
         }
     }
 
     /// Return the `Rawlink` and replace with `Rawlink::none()`
     fn take(&mut self) -> Rawlink<T> {
-        replace(self, Rawlink::none())
+        mem::replace(self, Rawlink::none())
     }
 }
 
@@ -159,7 +158,7 @@ impl<T> DList<T> {
             Some(ref mut head) => {
                 new_head.prev = Rawlink::none();
                 head.prev = Rawlink::some(new_head);
-                swap(head, &mut new_head);
+                mem::swap(head, &mut new_head);
                 head.next = Some(new_head);
             }
         }
@@ -317,7 +316,7 @@ impl<T> DList<T> {
     /// O(1)
     #[inline]
     pub fn prepend(&mut self, mut other: DList<T>) {
-        swap(self, &mut other);
+        mem::swap(self, &mut other);
         self.append(other);
     }
 

src/libcollections/enum_set.rs

@@ -137,7 +137,7 @@ impl<E:CLike> Iterator<E> for Items<E> {
 #[cfg(test)]
 mod test {
 
-    use std::cast;
+    use std::mem;
 
     use enum_set::{EnumSet, CLike};
 
@@ -153,7 +153,7 @@ mod test {
         }
 
         fn from_uint(v: uint) -> Foo {
-            unsafe { cast::transmute(v) }
+            unsafe { mem::transmute(v) }
         }
     }
 

src/libcollections/lru_cache.rs

@@ -37,7 +37,6 @@
 //! assert!(cache.get(&2).is_none());
 //! ```
 
-use std::cast;
 use std::container::Container;
 use std::hash::Hash;
 use std::fmt;
@@ -93,7 +92,7 @@ impl<K: Hash + TotalEq, V> LruCache<K, V> {
         let cache = LruCache {
             map: HashMap::new(),
             max_size: capacity,
-            head: unsafe{ cast::transmute(box mem::uninit::<LruEntry<K, V>>()) },
+            head: unsafe{ mem::transmute(box mem::uninit::<LruEntry<K, V>>()) },
         };
         unsafe {
             (*cache.head).next = cache.head;
@@ -241,11 +240,11 @@ impl<K: Hash + TotalEq, V> Mutable for LruCache<K, V> {
 impl<K, V> Drop for LruCache<K, V> {
     fn drop(&mut self) {
         unsafe {
-            let node: Box<LruEntry<K, V>> = cast::transmute(self.head);
+            let node: Box<LruEntry<K, V>> = mem::transmute(self.head);
             // Prevent compiler from trying to drop the un-initialized field in the sigil node.
             let box LruEntry { key: k, value: v, .. } = node;
-            cast::forget(k);
-            cast::forget(v);
+            mem::forget(k);
+            mem::forget(v);
         }
     }
 }

src/libcore/any.rs

@@ -20,7 +20,7 @@
 //! value. `Box<Any>` adds the `move` method, which will unwrap a `Box<T>` from the object.  See
 //! the extension traits (`*Ext`) for the full details.
 
-use cast::{transmute, transmute_copy};
+use mem::{transmute, transmute_copy};
 use option::{Option, Some, None};
 use owned::Box;
 use raw::TraitObject;