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

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

    #[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<AnotherTrait>`. The Trait Objects chapter of the Book contains more details about the precise nature of these internals.

`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 Copy for TraitObject`
[src]

### `impl Clone for TraitObject`
[src]

#### `fn clone(&self) -> TraitObject`

Returns a copy of the value. Read more

#### `fn clone_from(&mut self, source: &Self)`
1.0.0

Performs copy-assignment from `source`. Read more

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