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_placeimpl (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 moresource§impl<Dyn> Debug for DynMetadata<Dyn>where
    Dyn: ?Sized,
 
impl<Dyn> Debug for DynMetadata<Dyn>where
    Dyn: ?Sized,
source§impl<Dyn> Hash for DynMetadata<Dyn>where
    Dyn: ?Sized,
 
impl<Dyn> Hash for DynMetadata<Dyn>where
    Dyn: ?Sized,
source§impl<Dyn> Ord for DynMetadata<Dyn>where
    Dyn: ?Sized,
 
impl<Dyn> Ord for DynMetadata<Dyn>where
    Dyn: ?Sized,
source§fn cmp(&self, other: &DynMetadata<Dyn>) -> Ordering
 
fn cmp(&self, other: &DynMetadata<Dyn>) -> Ordering
1.21.0 · source§fn max(self, other: Self) -> Selfwhere
    Self: Sized,
 
fn max(self, other: Self) -> Selfwhere
    Self: Sized,
source§impl<Dyn> PartialEq for DynMetadata<Dyn>where
    Dyn: ?Sized,
 
impl<Dyn> PartialEq for DynMetadata<Dyn>where
    Dyn: ?Sized,
source§fn eq(&self, other: &DynMetadata<Dyn>) -> bool
 
fn eq(&self, other: &DynMetadata<Dyn>) -> bool
self and other values to be equal, and is used
by ==.source§impl<Dyn> PartialOrd for DynMetadata<Dyn>where
    Dyn: ?Sized,
 
impl<Dyn> PartialOrd for DynMetadata<Dyn>where
    Dyn: ?Sized,
source§fn partial_cmp(&self, other: &DynMetadata<Dyn>) -> Option<Ordering>
 
fn partial_cmp(&self, other: &DynMetadata<Dyn>) -> Option<Ordering>
1.0.0 · source§fn le(&self, other: &Rhs) -> bool
 
fn le(&self, other: &Rhs) -> bool
self and other) and is used by the <=
operator. Read more