Fix E0605: Mismatched Return Type in Rust

Sat, 08 Aug 2026 00:44:04 +0800

1. Symptoms

When the Rust compiler encounters error E0605, you will see output similar to the following:

error[E0605]: expected `()`, found `(_)`
 --> src/main.rs:4:20
  |
4 | fn bad_function() { return (1, 2); }
  |                     ^^^^^^^^^^^^^ expected `()`, found a tuple

error[E0605]: expected `bool`, found `(_, _)`
 --> src/main.rs:8:18
  |
8 | fn another_bad() -> bool { (true, false) }
  |                    ----      ^^^^^^^^^ expected `bool`, found a tuple

The compiler clearly indicates which type was expected based on the function signature and which type was actually found in the return expression. In the first example, a function with no return value (unit type ()) attempts to return a tuple (i32, i32). In the second example, a function declaring a return type of bool tries to return a tuple instead.

E0605 on ErrorVault — Developer Error Code Dictionary

Fix E0605: Mismatched Return Type in Rust

1. Symptoms