Understanding Rust Error E0124: Duplicate Field Names in Structs

Introduction to Rust Error E0124

Rust Error E0124 occurs when you declare a struct with two or more fields having the same name. This error is raised because each field in a struct must have a unique identifier.

Example of Erroneous Code

In the official documentation's example, the error occurs when the Foo struct is declared with two fields named field1:

struct Foo {
    field1: i32,
    field1: i32, // error: field is already declared
}

Solving Rust Error E0124

To resolve Error E0124, you need to ensure that all fields in the struct have distinct names. In the corrected example below, the second field is renamed to field2:

struct Foo {
    field1: i32,
    field2: i32, // ok!
}

More Complex Example

In a more complex struct, it's possible to accidentally use the same name for nested fields. This example demonstrates a similar error involving nested structs:

struct Bar {
    a: i32,
    b: i32,
}

struct Foo {
    field1: Bar,
    field2: i32,
    a: i32, // error: field is already declared
}

Conclusion

To avoid Rust Error E0124, make sure to use unique names for all fields in your struct declarations. This prevents ambiguity and simplifies your code.