| The coerced type does not outlive the value being coerced to. |
| |
| Example of erroneous code: |
| |
| ```compile_fail,E0476 |
| #![feature(coerce_unsized)] |
| #![feature(unsize)] |
| |
| use std::marker::Unsize; |
| use std::ops::CoerceUnsized; |
| |
| // error: lifetime of the source pointer does not outlive lifetime bound of the |
| // object type |
| impl<'a, 'b, T, S> CoerceUnsized<&'a T> for &'b S where S: Unsize<T> {} |
| ``` |
| |
| During a coercion, the "source pointer" (the coerced type) did not outlive the |
| "object type" (value being coerced to). In the above example, `'b` is not a |
| subtype of `'a`. This error can currently only be encountered with the unstable |
| `CoerceUnsized` trait which allows custom coercions of unsized types behind a |
| smart pointer to be implemented. |
