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Understanding Rust Error E0184: Conflicting Traits

Introduction to Rust Error E0184

Rust Error E0184 occurs when both the Copy and Drop traits are implemented on the same type. The interaction between these traits can lead to memory safety issues (see issue #20126), and therefore, the implementation of both traits on a single type is disallowed.

Example of Rust Error E0184

Consider the following erroneous code example:

#![allow(unused)]
fn main() {
#[derive(Copy)]
struct Foo; // error!

impl Drop for Foo {
    fn drop(&mut self) {
    }
}
}

This code generates Rust Error E0184 because the type `Foo` has both the Copy trait derived and a Drop trait implementation.

Resolving Rust Error E0184

To resolve Rust Error E0184, you must remove either the Copy or Drop trait from the type. Depending on the requirements of your application, you may have to adjust the type's behavior accordingly.

Solution: Removing the Copy Trait

If your type needs a custom Drop implementation, remove the Copy trait, and use the Clone trait if necessary. The revised code will look like this:

#![allow(unused)]
fn main() {
#[derive(Clone)]
struct Foo;

impl Drop for Foo {
    fn drop(&mut self) {
        // custom drop code
    }
}
}

Solution: Removing the Drop Trait

If the type's Drop implementation is not necessary and you prefer to keep the Copy trait, simply remove the Drop trait. The updated code will resemble the following:

#![allow(unused)]
fn main() {
#[derive(Copy, Clone)]
struct Foo; // no error
}

Conclusion

Rust Error E0184 arises when a type has both the Copy and Drop traits implemented, which can lead to memory safety issues. To resolve this error, remove either the Copy or Drop trait, and adjust your implementation as needed. Remember to consider the Clone trait if a custom Drop implementation is required.

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