Struct std::ptr::DynMetadata

pub struct DynMetadata<Dyn>
where
    Dyn: ?Sized,
{ /* private fields */ }

🔬This is a nightly-only experimental API. (ptr_metadata #81513)

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

impl<Dyn> DynMetadata<Dyn>

where Dyn: ?Sized,

pub fn size_of(self) -> usize

🔬This is a nightly-only experimental API. (ptr_metadata #81513)

Returns the size of the type associated with this vtable.

pub fn align_of(self) -> usize

🔬This is a nightly-only experimental API. (ptr_metadata #81513)

Returns the alignment of the type associated with this vtable.

pub fn layout(self) -> Layout

🔬This is a nightly-only experimental API. (ptr_metadata #81513)

Returns the size and alignment together as a Layout

Trait Implementations

impl<Dyn> Clone for DynMetadata<Dyn>

where Dyn: ?Sized,

fn clone(&self) -> DynMetadata<Dyn>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<Dyn> Debug for DynMetadata<Dyn>

where Dyn: ?Sized,

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

Formats the value using the given formatter.

impl<Dyn> Hash for DynMetadata<Dyn>

where Dyn: ?Sized,

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

where H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<Dyn> Ord for DynMetadata<Dyn>

where Dyn: ?Sized,

fn cmp(&self, other: &DynMetadata<Dyn>) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized + PartialOrd,

Restrict a value to a certain interval.

impl<Dyn> PartialEq for DynMetadata<Dyn>

where Dyn: ?Sized,

fn eq(&self, other: &DynMetadata<Dyn>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<Dyn> PartialOrd for DynMetadata<Dyn>

where Dyn: ?Sized,

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

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl<Dyn> Copy for DynMetadata<Dyn>

where Dyn: ?Sized,

impl<Dyn> Eq for DynMetadata<Dyn>

where Dyn: ?Sized,

impl<Dyn> Send for DynMetadata<Dyn>

where Dyn: ?Sized,

impl<Dyn> Sync for DynMetadata<Dyn>

where Dyn: ?Sized,

impl<Dyn> Unpin for DynMetadata<Dyn>

where Dyn: ?Sized,