DynMetadata in std::ptr - Rust
Description: The metadata for a `Dyn = dyn SomeTrait` trait object type.

## DynMetadata

# Struct DynMetadata

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

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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> Clone for DynMetadata<Dyn>
where Dyn: ?Sized,

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

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

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

Performs copy-assignment from `source`. Read more
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### impl<Dyn> Debug for DynMetadata<Dyn>
where Dyn: ?Sized,

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

Formats the value using the given formatter. Read more
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### impl<Dyn> Hash for DynMetadata<Dyn>
where Dyn: ?Sized,

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

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

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

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

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#### fn cmp(&self, other: &DynMetadata<Dyn>) -> 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
1.50.0 · Source§

#### 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> PartialEq for DynMetadata<Dyn>
where Dyn: ?Sized,

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#### fn eq(&self, other: &DynMetadata<Dyn>) -> 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> PartialOrd for DynMetadata<Dyn>
where Dyn: ?Sized,

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#### fn partial_cmp(&self, other: &DynMetadata<Dyn>) -> 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
1.0.0 · Source§

#### 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> Copy for DynMetadata<Dyn>
where Dyn: ?Sized,

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

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

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

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

## 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> ToOwned for T
where T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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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.