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

    pub struct TraitObject {
        pub data: *mut (),
        pub vtable: *mut (),
    }

Unstable (`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 `Repr` implementation for `TraitObject` because 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)] fn main() { use std::mem; use std::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 like we constructed a trait object out of // `other_value` directly assert_eq!(synthesized.bar(), 457); }

    #![feature(raw)]

    use std::mem;
    use std::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 like we constructed a trait object out of
    // `other_value` directly
    assert_eq!(synthesized.bar(), 457);

## Fields

`data` | Unstable (`raw` #27751)
`vtable` | Unstable (`raw` #27751)

## Trait Implementations

### Derived Implementations

### `impl Clone for TraitObject`

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

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

### `impl Copy for TraitObject`

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