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Understanding Rust Error E0062: Duplicate Field in Struct or Enum Variant

What is Rust Error E0062?

Rust Error E0062 occurs when a field in a struct or struct-like enum variant is specified more than once during instantiation. Each field should be specified exactly once.

Erroneous Code Example

struct Foo {
    x: i32,
}

fn main() {
    let x = Foo {
                x: 0,
                x: 0, // error: field `x` specified more than once
            };
}

In the example above, the field `x` is specified twice. The correct version should look like this:

Correct Code Example

struct Foo {
    x: i32,
}

fn main() {
    let x = Foo { x: 0 }; // ok!
}

Struct-like Enum Variant Example

The same error can occur with struct-like enum variants. Consider the following erroneous code:

enum MyEnum {
    Variant { x: i32, y: i32 }
}

fn main() {
    let value = MyEnum::Variant { x: 1, y: 2, x: 1 }; // error: field `x` specified more than once
}

The error here is due to specifying the `x` field twice in the `MyEnum::Variant` instantiation. The corrected version should look like this:

Correct Enum Variant Example

enum MyEnum {
    Variant { x: i32, y: i32 }
}

fn main() {
    let value = MyEnum::Variant { x: 1, y: 2 }; // ok!
}

Summary

Rust Error E0062 is caused by specifying a field more than once during the instantiation of a struct or struct-like enum variant. To fix this error, ensure each field is specified only once.

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