Fix E0390: Rust Method Self Parameter Mismatch Between Trait and Implementation

Fri, 31 Jul 2026 05:32:04 +0800

1. Symptoms

When the Rust compiler encounters error E0390, it produces a diagnostic message that clearly indicates a mismatch between the trait definition and its implementation. The compiler output typically appears as follows:

error[E0390]: method `method_name` has a `&self` declaration in the impl, but not in the trait
  --> src/main.rs:10:1
   |
5  |     fn method_name(&self);
   |     ------------------- the trait has no `&self` declaration
...
10 |     fn method_name(&self) { ... }
   |     ^^^^^^^^^^^^^^^^^^^^^ the impl has a `&self` declaration

Alternatively, you may encounter the inverse situation where the trait declares &self but the implementation does not:

E0390 on ErrorVault — Developer Error Code Dictionary

Fix E0390: Rust Method Self Parameter Mismatch Between Trait and Implementation

1. Symptoms