Struct std::ptr::DynMetadata
source · pub struct DynMetadata<Dyn>where
Dyn: ?Sized,{ /* private fields */ }
ptr_metadata
#81513)Expand description
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).
Implementations§
source§impl<Dyn> DynMetadata<Dyn>where
Dyn: ?Sized,
impl<Dyn> DynMetadata<Dyn>where
Dyn: ?Sized,
sourcepub fn size_of(self) -> usize
🔬This is a nightly-only experimental API. (ptr_metadata
#81513)
pub fn size_of(self) -> usize
ptr_metadata
#81513)Returns the size of the type associated with this vtable.
Trait Implementations§
source§impl<Dyn> Clone for DynMetadata<Dyn>where
Dyn: ?Sized,
impl<Dyn> Clone for DynMetadata<Dyn>where
Dyn: ?Sized,
source§fn clone(&self) -> DynMetadata<Dyn>
fn clone(&self) -> DynMetadata<Dyn>
1.0.0 · source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source
. Read more