# Struct DynMetadata

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    pub struct DynMetadata<Dyn: PointeeSized> { /* private fields */ }

🔬This is a nightly-only experimental API. (`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§

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### impl<Dyn: PointeeSized> DynMetadata<Dyn>

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#### 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.

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#### 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.

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#### 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§

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

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#### fn clone(&self) -> Self

Returns a duplicate of the value. Read more
1.0.0 · Source§

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

Performs copy-assignment from `source`. Read more
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### impl<Dyn: PointeeSized> Debug for DynMetadata<Dyn>

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

Formats the value using the given formatter. Read more
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### impl<Dyn: PointeeSized> Hash for DynMetadata<Dyn>

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

Feeds this value into the given `Hasher`. Read more
1.3.0 · Source§

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

Feeds a slice of this type into the given `Hasher`. Read more
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### impl<Dyn: PointeeSized> Ord for DynMetadata<Dyn>

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

This method returns an `Ordering` between `self` and `other`. Read more
1.21.0 · Source§

#### fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 · Source§

#### fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
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#### fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized,

Restrict a value to a certain interval. Read more
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### impl<Dyn: PointeeSized> PartialEq for DynMetadata<Dyn>

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

Tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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### impl<Dyn: PointeeSized> PartialOrd for DynMetadata<Dyn>

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

This method returns an ordering between `self` and `other` values if one exists. Read more
1.0.0 · Source§

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

Tests less than (for `self` and `other`) and is used by the `<` operator. Read more
1.0.0 · Source§

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

Tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more
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#### fn gt(&self, other: &Rhs) -> bool

Tests greater than (for `self` and `other`) and is used by the `>` operator. Read more
1.0.0 · Source§

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

Tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more
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### impl<Dyn: PointeeSized> Copy for DynMetadata<Dyn>

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

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

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

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

## Auto Trait Implementations§

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

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

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

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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

Mutably borrows from an owned value. Read more
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### impl<T> CloneToUninit for T
where T: Clone,

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

🔬This is a nightly-only experimental API. (`clone_to_uninit` #126799)
Performs copy-assignment from `self` to `dest`. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

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

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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.