Merge pull request #3170 from SimonSapin/trait-object-transmute

Transmute std::raw::TraitObject rather than (some) custom tuples/structs

src/components/layout/flow.rs

@@ -57,6 +57,7 @@ use std::mem;
 use std::num::Zero;
 use std::fmt;
 use std::iter::Zip;
+use std::raw;
 use std::sync::atomics::{AtomicUint, Relaxed, SeqCst};
 use std::slice::MutItems;
 use style::computed_values::{clear, position, text_align};
@@ -274,8 +275,8 @@ pub trait Flow: fmt::Show + ToString + Share {
 #[inline(always)]
 pub fn base<'a>(this: &'a Flow) -> &'a BaseFlow {
     unsafe {
-        let (_, ptr): (uint, &BaseFlow) = mem::transmute(this);
-        ptr
+        let obj = mem::transmute::<&'a Flow, raw::TraitObject>(this);
+        mem::transmute::<*mut (), &'a BaseFlow>(obj.data)
     }
 }
 
@@ -287,8 +288,8 @@ pub fn imm_child_iter<'a>(flow: &'a Flow) -> FlowListIterator<'a> {
 #[inline(always)]
 pub fn mut_base<'a>(this: &'a mut Flow) -> &'a mut BaseFlow {
     unsafe {
-        let (_, ptr): (uint, &mut BaseFlow) = mem::transmute(this);
-        ptr
+        let obj = mem::transmute::<&'a mut Flow, raw::TraitObject>(this);
+        mem::transmute::<*mut (), &'a mut BaseFlow>(obj.data)
     }
 }
 

src/components/layout/flow_list.rs

@@ -11,16 +11,14 @@ use flow_ref::FlowRef;
 use std::kinds::marker::ContravariantLifetime;
 use std::mem;
 use std::ptr;
+use std::raw;
 
 pub type Link = Option<FlowRef>;
 
 
-// FIXME: use TraitObject instead of duplicating the type
 #[allow(raw_pointer_deriving)]
-#[deriving(Clone)]
 pub struct Rawlink<'a> {
-    vtable: *mut (),
-    obj: *mut (),
+    object: raw::TraitObject,
     marker: ContravariantLifetime<'a>,
 }
 
@@ -50,23 +48,29 @@ impl<'a> Rawlink<'a> {
     /// Like Option::None for Rawlink
     pub fn none() -> Rawlink<'static> {
         Rawlink {
-            vtable: ptr::mut_null(),
-            obj: ptr::mut_null(),
+            object: raw::TraitObject {
+                vtable: ptr::mut_null(),
+                data: ptr::mut_null(),
+            },
             marker: ContravariantLifetime,
         }
     }
 
     /// Like Option::Some for Rawlink
     pub fn some(n: &Flow) -> Rawlink {
-        unsafe { mem::transmute(n) }
+        unsafe {
+            Rawlink {
+                object: mem::transmute::<&Flow, raw::TraitObject>(n),
+                marker: ContravariantLifetime,
+            }
+        }
     }
 
     pub unsafe fn resolve_mut(&self) -> Option<&'a mut Flow> {
-        if self.obj.is_null() {
+        if self.object.data.is_null() {
             None
         } else {
-            let me: &mut Flow = mem::transmute_copy(self);
-            Some(me)
+            Some(mem::transmute_copy::<raw::TraitObject, &mut Flow>(&self.object))
         }
     }
 }

src/components/layout/flow_ref.rs

@@ -11,13 +11,12 @@ use flow;
 
 use std::mem;
 use std::ptr;
+use std::raw;
 use std::sync::atomics::SeqCst;
 
-// FIXME: This should probably be a wrapper on TraitObject.
 #[unsafe_no_drop_flag]
 pub struct FlowRef {
-    vtable: *const u8,
-    ptr: *const u8,
+    object: raw::TraitObject,
 }
 
 impl FlowRef {
@@ -25,7 +24,8 @@ impl FlowRef {
         unsafe {
             let result = {
                 let flow_ref: &mut Flow = flow;
-                mem::transmute(flow_ref)
+                let object = mem::transmute::<&mut Flow, raw::TraitObject>(flow_ref);
+                FlowRef { object: object }
             };
             mem::forget(flow);
             result
@@ -34,13 +34,13 @@ impl FlowRef {
 
     pub fn get<'a>(&'a self) -> &'a Flow {
         unsafe {
-            mem::transmute_copy(self)
+            mem::transmute_copy::<raw::TraitObject, &'a Flow>(&self.object)
         }
     }
 
     pub fn get_mut<'a>(&'a mut self) -> &'a mut Flow {
         unsafe {
-            mem::transmute_copy(self)
+            mem::transmute_copy::<raw::TraitObject, &'a mut Flow>(&self.object)
         }
     }
 }
@@ -48,19 +48,22 @@ impl FlowRef {
 impl Drop for FlowRef {
     fn drop(&mut self) {
         unsafe {
-            if self.vtable == ptr::null() {
+            if self.object.vtable.is_null() {
                 return
             }
             if flow::base(self.get()).ref_count().fetch_sub(1, SeqCst) > 1 {
                 return
             }
             let flow_ref: FlowRef = mem::replace(self, FlowRef {
-                vtable: ptr::null(),
-                ptr: ptr::null(),
+                object: raw::TraitObject {
+                    vtable: ptr::mut_null(),
+                    data: ptr::mut_null(),
+                }
             });
-            drop(mem::transmute::<FlowRef,Box<Flow>>(flow_ref));
-            self.vtable = ptr::null();
-            self.ptr = ptr::null();
+            drop(mem::transmute::<raw::TraitObject, Box<Flow>>(flow_ref.object));
+            mem::forget(flow_ref);
+            self.object.vtable = ptr::mut_null();
+            self.object.data = ptr::mut_null();
         }
     }
 }
@@ -70,8 +73,10 @@ impl Clone for FlowRef {
         unsafe {
             drop(flow::base(self.get()).ref_count().fetch_add(1, SeqCst));
             FlowRef {
-                vtable: self.vtable,
-                ptr: self.ptr,
+                object: raw::TraitObject {
+                    vtable: self.object.vtable,
+                    data: self.object.data,
+                }
             }
         }
     }