std::raw::TraitObject - Rust
Description: API documentation for the Rust `TraitObject` struct in crate `std`.
Keywords: rust, rustlang, rust-lang, TraitObject

# [−][src]Struct std::raw::TraitObject

    #[repr(C)]
    pub struct TraitObject {
        pub data: *mut (),
        pub vtable: *mut (),
    }

🔬 This is a nightly-only experimental API. (`raw` #27751)

The representation of a trait object like `&SomeTrait`.

This struct has the same layout as types like `&SomeTrait` and `Box<dyn AnotherTrait>`.

`TraitObject` is guaranteed to match layouts, but it is not the type of trait objects (e.g. the fields are not directly accessible on a `&SomeTrait`) nor does it control that layout (changing the definition will not change the layout of a `&SomeTrait`). It is only designed to be used by unsafe code that needs to manipulate the low-level details.

There is no way to refer to all trait objects generically, so the only way to create values of this type is with functions like `std::mem::transmute`. Similarly, the only way to create a true trait object from a `TraitObject` value is with `transmute`.

Synthesizing a trait object with mismatched types—one where the vtable does not correspond to the type of the value to which the data pointer points—is highly likely to lead to undefined behavior.

# Examples

    #![feature(raw)]

    use std::{mem, raw};

    // an example trait
    trait Foo {
        fn bar(&self) -> i32;
    }

    impl Foo for i32 {
        fn bar(&self) -> i32 {
             *self + 1
        }
    }

    let value: i32 = 123;

    // let the compiler make a trait object
    let object: &Foo = &value;

    // look at the raw representation
    let raw_object: raw::TraitObject = unsafe { mem::transmute(object) };

    // the data pointer is the address of `value`
    assert_eq!(raw_object.data as *const i32, &value as *const _);

    let other_value: i32 = 456;

    // construct a new object, pointing to a different `i32`, being
    // careful to use the `i32` vtable from `object`
    let synthesized: &Foo = unsafe {
         mem::transmute(raw::TraitObject {
             data: &other_value as *const _ as *mut (),
             vtable: raw_object.vtable,
         })
    };

    // it should work just as if we had constructed a trait object out of
    // `other_value` directly
    assert_eq!(synthesized.bar(), 457);Run

## Fields

`data: *mut ()`
🔬 This is a nightly-only experimental API. (`raw` #27751)
`vtable: *mut ()`
🔬 This is a nightly-only experimental API. (`raw` #27751)

## Trait Implementations

###

`impl Clone for TraitObject`

[src]

####

`fn clone(&self) -> TraitObject`

[src]

Returns a copy of the value. Read more

####

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

1.0.0
[src]

Performs copy-assignment from `source`. Read more

###

`impl Copy for TraitObject`

[src]

## Auto Trait Implementations

###

`impl !Send for TraitObject`

###

`impl !Sync for TraitObject`

## Blanket Implementations

###

`impl<T> From for T`

[src]

####

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

[src]

Performs the conversion.

###

`impl<T, U> TryFrom for T where T: From<U>,`

[src]

#### `type Error = !`

🔬 This is a nightly-only experimental API. (`try_from` #33417)

The type returned in the event of a conversion error.

####

`fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`

[src]

🔬 This is a nightly-only experimental API. (`try_from` #33417)

Performs the conversion.

###

`impl<T, U> TryInto for T where U: TryFrom<T>,`

[src]

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

🔬 This is a nightly-only experimental API. (`try_from` #33417)

The type returned in the event of a conversion error.

####

`fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>`

[src]

🔬 This is a nightly-only experimental API. (`try_from` #33417)

Performs the conversion.

###

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

[src]

####

`fn into(self) -> U`

[src]

Performs the conversion.

###

`impl<T> Borrow for T where T: ?Sized,`

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####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`

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

[src]

Immutably borrows from an owned value. Read more

###

`impl<T> BorrowMut for T where T: ?Sized,`

[src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`

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

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Mutably borrows from an owned value. Read more

###

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

[src]

####

`fn get_type_id(&self) -> TypeId`

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🔬 This is a nightly-only experimental API. (`get_type_id` #27745)

this method will likely be replaced by an associated static

Gets the `TypeId` of `self`. Read more

###

`impl<T> ToOwned for T where T: Clone,`

[src]

#### `type Owned = T`

####

`fn to_owned(&self) -> T`

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Creates owned data from borrowed data, usually by cloning. Read more

####

`fn clone_into(&self, target: &mut T)`

[src]

🔬 This is a nightly-only experimental API. (`toowned_clone_into` #41263)

recently added

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

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