Fix E0161: the trait bound `Drop + Sized` is not satisfied

Wed, 22 Jul 2026 10:20:04 +0800

1. Symptoms

When the Rust compiler encounters error E0161, you will see output similar to the following in your terminal or IDE:

error[E0161]: the trait bound `Drop + Sized` is not satisfied
  --> src/main.rs:10:5
   |
10 |     fn drop(&mut self) { }
   |     ^^^^^^ unsized types have no automatic `Drop` implementations
   |
   = note: unsized types have no automatic `Drop` implementations
   = note: this error occurs because the type has a `Drop` implementation in the
     standard library, but not all its fields implement `Sized`
     = help: consider moving the `Drop` implementation to a wrapper type

The error message indicates that you are attempting to use a feature that requires the Sized bound, but the type in question is unsized. Unsized types in Rust include trait objects (dyn Trait), slices ([T]), and the string slice type (str). These types do not have a known size at compile time, which prevents certain operations that require knowing the exact memory layout of a type.

Sized Trait on ErrorVault — Developer Error Code Dictionary

Fix E0161: the trait bound `Drop + Sized` is not satisfied

1. Symptoms