Rust errors / Ownership and borrowing
Rust compiler error · checked with rustc 1.99.0
Rust error E0476: lifetime of the source pointer does not outlive lifetime bound of the object type
What it meansThe coerced type does not outlive the value being coerced to.
What rustc prints
error[E0476]: lifetime of the source pointer does not outlive lifetime bound of the object type --> main.rs:9:1 | 9 | impl<'a, 'b, T, S> CoerceUnsized<&'a T> for &'b S where S: Unsize<T> {} | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | note: object type is valid for the lifetime `'a` as defined here --> main.rs:9:6 | 9 | impl<'a, 'b, T, S> CoerceUnsized<&'a T> for &'b S where S: Unsize<T> {} | ^^ note: source pointer is only valid for the lifetime `'b` as defined here --> main.rs:9:10 | 9 | impl<'a, 'b, T, S> CoerceUnsized<&'a T> for &'b S where S: Unsize<T> {} | ^^
Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.
The compiler team's explanation
The coerced type does not outlive the value being coerced to.
Example of erroneous code:
#![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.
From rustc --explain E0476 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.
Related errors
- E0382borrow of moved value
- E0499cannot borrow as mutable more than once at a time
- E0502cannot borrow as mutable because it is also borrowed as immutable
- E0106missing lifetime specifier
- E0384cannot assign twice to immutable variable
- E0392type parameter `T` is never used
- E0478A lifetime bound was not satisfied
- E0491in type `&'a Foo<'b>`, reference has a longer lifetime than the data it references
Up next
Often hit nextE0382: borrow of moved valueA related error from the same family.Read it next →Did this answer your question?