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Understanding Rust Error E0071

Rust Error E0071 Explained

Rust Error E0071 occurs when a structure-literal syntax is used to create an item that is not a structure, enum variant, or a union type. This error usually stems from using an incorrect syntax for the data type you are trying to create.

Example of Rust Error E0071

Consider the following erroneous code snippet:

#![allow(unused)]
fn main() {
    type U32 = u32;
    let t = U32 { value: 4 }; // error: expected struct, variant or union type,
                              // found builtin type `u32`
}

In the code above, the programmer attempts to initialize a variable 't' as an instance of 'U32' using a structure-literal syntax, i.e., 'U32 { value: 4 }'. However, 'U32' is an alias for the built-in type 'u32', which is not a structure, enum variant, or union type. As a result, Rust throws Error E0071.

How to Fix Rust Error E0071

To fix Rust Error E0071, ensure that the name of the data type is spelled correctly and that the correct form of initializer is used. In our example, the code can be fixed in two ways:

1. Correct the initializer syntax:

#![allow(unused)]
fn main() {
    type U32 = u32;
    let t: U32 = 4;
}

In this fix, the initializer syntax is corrected by simply assigning the value 4 to the variable 't' with the type 'U32'.

2. Define a custom structure to match the initializer syntax:

#![allow(unused)]
fn main() {
    struct U32 { value: u32 }
    let t = U32 { value: 4 };
}

Here, a custom structure 'U32' is defined with a field 'value' of type 'u32'. Consequently, the structure-literal syntax used to initialize the variable 't' becomes valid.

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