Dyn Trait on ErrorVault — Developer Error Code Dictionary

Fix E0661: method call on field of unsized type

Tue, 28 Jul 2026 05:32:04 +0800

1. Symptoms

The Rust compiler emits error E0661 when you attempt to invoke a method on a struct or enum field that has an unsized type. This error manifests during compilation and prevents the binary from being built, regardless of whether the method being called is defined on the field type or inherited through a trait implementation.

The compiler produces output similar to the following when this error is encountered:

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.

Fix E0616: Attempt to Call Method Not Found on Trait Object

Wed, 15 Jul 2026 22:20:04 +0800

Fix E0616: Attempt to Call Method Not Found on Trait Object

Rust’s trait system provides powerful abstraction capabilities through both static and dynamic dispatch. When working with trait objects via dyn Trait, you encounter a fundamental limitation: only the methods declared in the trait definition are available at runtime. Error E0616 surfaces when your code attempts to call a method that exists on the underlying concrete type but was not included in the trait definition. This creates a clear separation between what the concrete type can do and what the trait object can expose, enforcing the boundaries of dynamic dispatch.