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Understanding Rust Error E0025: Field Bound Multiple Times in a Pattern

What is Rust Error E0025?

Rust error E0025 occurs when a field in a struct is bound multiple times within a single pattern. In Rust, each field of a struct can only be bound once in a pattern, and attempting to bind the same field more than once will result in this error.

Example of Erroneous Code

struct Foo {
    a: u8,
    b: u8,
}

fn main(){
    let x = Foo { a:1, b:2 };

    let Foo { a: x, a: y } = x;
    // error: field `a` bound multiple times in the pattern
}

In the above example, field 'a' is being bound two times in the pattern. This is against Rust's rule of binding each field only once in a pattern, and the compiler will throw error E0025.

How to Fix Rust Error E0025

To fix Rust Error E0025, ensure that each field is bound only once in a pattern. Double-check your code for any attempts to bind the same field more than once, and remove or modify these duplicate bindings. It's also possible that a similar field name was misspelled, causing the duplication.

Example of Corrected Code

struct Foo {
    a: u8,
    b: u8,
}

fn main(){
    let x = Foo { a:1, b:2 };

    let Foo { a: x, b: y } = x; // ok!
}

In this corrected example, each field 'a' and 'b' is bound only once in the pattern, complying with Rust's rule and avoiding error E0025.

Common Causes for Rust Error E0025

1. Accidentally typing the same field name twice in a pattern when destructuring a struct, instead of using unique field names. 2. A misspelled field name that makes it seem like a duplicate, when it should have been a different field. Double-check for typos in your field names. 3. Unintentionally repeating a field name while copy-pasting code. Make sure to modify duplicated fields accordingly.