Struct `DynMetadata`

pub struct DynMetadata<Dyn: PointeeSized> { pub(in ::ptr::metadata) _vtable_ptr: NonNull<VTable>, pub(in ::ptr::metadata) _phantom: PhantomData<Dyn> }

The metadata for a Dyn = dyn SomeTrait trait object type.

It is a pointer to a vtable (virtual call table) that represents all the necessary information to manipulate the concrete type stored inside a trait object. The vtable notably contains:

type size
type alignment
a pointer to the type’s drop_in_place impl (may be a no-op for plain-old-data)
pointers to all the methods for the type’s implementation of the trait

Note that the first three are special because they’re necessary to allocate, drop, and deallocate any trait object.

It is possible to name this struct with a type parameter that is not a dyn trait object (for example DynMetadata<u64>) but not to obtain a meaningful value of that struct.

Note that while this type implements PartialEq, comparing vtable pointers is unreliable: pointers to vtables of the same type for the same trait can compare inequal (because vtables are duplicated in multiple codegen units), and pointers to vtables of different types/traits can compare equal (since identical vtables can be deduplicated within a codegen unit).

Fields

_vtable_ptr: NonNull<VTable>
_phantom: PhantomData<Dyn>

Implementations

`impl<Dyn: PointeeSized> DynMetadata<Dyn>`

fn vtable_ptr(self) -> *const VTable: When DynMetadata appears as the metadata field of a wide pointer, the rustc_middle layout computation does magic and the resulting layout is not a FieldsShape::Aggregate, instead it is a FieldsShape::Primitive. This means that the same type can have different layout depending on whether it appears as the metadata field of a wide pointer or as a stand-alone type, which understandably confuses codegen and leads to ICEs when trying to project to a field of DynMetadata. To work around that issue, we use transmute instead of using a field projection.
fn size_of(self) -> usize: Returns the size of the type associated with this vtable.
fn align_of(self) -> usize: Returns the alignment of the type associated with this vtable.
fn layout(self) -> Layout: Returns the size and alignment together as a Layout

Trait Implementations

`impl<Dyn: PointeeSized> Clone for DynMetadata<Dyn>`

fn clone(&self) -> Self

`impl<Dyn: PointeeSized> Copy for DynMetadata<Dyn>`

`impl<Dyn: PointeeSized> Debug for DynMetadata<Dyn>`

fn fmt(&self, f: &mut Formatter<'_>) -> Result

`impl<Dyn: PointeeSized> Eq for DynMetadata<Dyn>`

`impl<Dyn: PointeeSized> Hash for DynMetadata<Dyn>`

fn hash<H: Hasher>(&self, hasher: &mut H)

`impl<Dyn: PointeeSized> Ord for DynMetadata<Dyn>`

fn cmp(&self, other: &Self) -> Ordering

`impl<Dyn: PointeeSized> PartialEq for DynMetadata<Dyn>`

fn eq(&self, other: &Self) -> bool

`impl<Dyn: PointeeSized> PartialOrd for DynMetadata<Dyn>`

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

`impl<Dyn: PointeeSized> Send for DynMetadata<Dyn>`

`impl<Dyn: PointeeSized> Sync for DynMetadata<Dyn>`

`impl<Dyn: PointeeSized> TrivialClone for DynMetadata<Dyn>`

`impl<Dyn: PointeeSized> Unpin for DynMetadata<Dyn>`

Auto Trait Implementations

`impl<Dyn> !RefUnwindSafe for DynMetadata<Dyn>`

`impl<Dyn> !UnwindSafe for DynMetadata<Dyn>`

`impl<Dyn> Freeze for DynMetadata<Dyn> where PhantomData<Dyn>: Freeze, Dyn: ?Sized,`

`impl<Dyn> UnsafeUnpin for DynMetadata<Dyn> where PhantomData<Dyn>: UnsafeUnpin, Dyn: ?Sized,`

Blanket Implementations

`impl<T> Any for DynMetadata<Dyn> where T: 'static + ?Sized,`

fn type_id(&self) -> TypeId

`impl<T> Borrow<T> for DynMetadata<Dyn> where T: ?Sized,`

fn borrow(&self) -> &T

`impl<T> BorrowMut<T> for DynMetadata<Dyn> where T: ?Sized,`

fn borrow_mut(&mut self) -> &mut T

`impl<T> CloneToUninit for DynMetadata<Dyn> where T: Clone,`

unsafe fn clone_to_uninit(&self, dest: *mut u8)

`impl<T> From<T> for DynMetadata<Dyn>`

fn from(t: T) -> T: Returns the argument unchanged.

`impl<T> Printable for DynMetadata<Dyn> where T: Copy + Debug,`

`impl<T> SizeHint for DynMetadata<Dyn> where T: ?Sized,`

fn lower_bound(&self) -> usize
fn upper_bound(&self) -> Option<usize>

`impl<T> SizedTypeProperties for DynMetadata<Dyn>`

`impl<T, U> Into<U> for DynMetadata<Dyn> where U: From<T>,`

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of [From]<T> for U chooses to do.

`impl<T, U> TryFrom<U> for DynMetadata<Dyn> where U: Into<T>,`

type Error = Infallible;
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

`impl<T, U> TryInto<U> for DynMetadata<Dyn> where U: TryFrom<T>,`

type Error = <U as TryFrom<T>>::Error;
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>