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Understanding Rust Error E0069

Rust Error E0069

Rust Error E0069 occurs when the compiler detects a function with a return type other than '()', but the function's body contains a 'return;' statement without any value.

Why this error occurs

In Rust, 'return;' is syntactically equivalent to 'return ();'. When using 'return;' without any value in a function that expects a return type, there is a type mismatch between the expected return type and the value being returned, causing error E0069.

Erroneous code example

#![allow(unused)]
fn main() {
    // error
    fn foo() -> u8 {
        return;
    }
}

In this example, function 'foo' has a return type 'u8', but the 'return;' statement doesn't provide any value which leads to a type mismatch and results in Rust Error E0069.

How to fix Rust Error E0069

To fix Rust Error E0069, you need to ensure that the value returned by the function matches its return type. You can either change the return type to '()' or update the return statement to provide a value of the expected type.

Solution 1: Change return type to '()'

If the function isn't expected to return any value, changing its return type to '()' will resolve the issue.

Example:

#![allow(unused)]
fn main() {
    fn foo() -> () {
        return;
    }
}

Solution 2: Provide a value in the return statement

If the function is expected to return a value of a specific type, you need to update the 'return;' statement to provide a value of that type.

Example:

#![allow(unused)]
fn main() {
    fn foo() -> u8 {
        return 42;
    }
}

Conclusion

Rust Error E0069 occurs when there is a type mismatch between the function's return type and the value being returned. To fix this error, ensure consistency between the return statement and the function's return type by either changing the return type to '()' or by providing a value of the correct type in the return statement.

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