diff options
Diffstat (limited to 'components/layout/flow.rs')
| -rw-r--r-- | components/layout/flow.rs | 14 |
1 files changed, 11 insertions, 3 deletions
diff --git a/components/layout/flow.rs b/components/layout/flow.rs index 8dad2104523..990e29e0238 100644 --- a/components/layout/flow.rs +++ b/components/layout/flow.rs @@ -65,11 +65,19 @@ use table_rowgroup::TableRowGroupFlow; use table_wrapper::TableWrapperFlow; use webrender_api::ClipAndScrollInfo; +/// This marker trait indicates that a type is a struct with `#[repr(C)]` whose first field +/// is of type `BaseFlow` or some type that also implements this trait. +/// +/// In other words, the memory representation of `BaseFlow` must be a prefix +/// of the memory representation of types implementing `HasBaseFlow`. +#[allow(unsafe_code)] +pub unsafe trait HasBaseFlow {} + /// Virtual methods that make up a float context. /// /// Note that virtual methods have a cost; we should not overuse them in Servo. Consider adding /// methods to `ImmutableFlowUtils` or `MutableFlowUtils` before adding more methods here. -pub trait Flow: fmt::Debug + Sync + Send + 'static { +pub trait Flow: HasBaseFlow + fmt::Debug + Sync + Send + 'static { // RTTI // // TODO(pcwalton): Use Rust's RTTI, once that works. @@ -451,7 +459,7 @@ pub trait Flow: fmt::Debug + Sync + Send + 'static { #[inline(always)] #[allow(unsafe_code)] -pub fn base<T: ?Sized + Flow>(this: &T) -> &BaseFlow { +pub fn base<T: ?Sized + HasBaseFlow>(this: &T) -> &BaseFlow { let ptr: *const T = this; let ptr = ptr as *const BaseFlow; unsafe { &*ptr } @@ -464,7 +472,7 @@ pub fn child_iter<'a>(flow: &'a Flow) -> FlowListIterator { #[inline(always)] #[allow(unsafe_code)] -pub fn mut_base<T: ?Sized + Flow>(this: &mut T) -> &mut BaseFlow { +pub fn mut_base<T: ?Sized + HasBaseFlow>(this: &mut T) -> &mut BaseFlow { let ptr: *mut T = this; let ptr = ptr as *mut BaseFlow; unsafe { &mut *ptr } |