How do I fix E0204 (the trait Copy cannot be implemented for this type)?

Derive Clone only, and clone explicitly: Or make the fields Copy: For example an id or a &'static str instead of a String.

Rust errors / Types and traits

Rust compiler error · checked with rustc 1.99.0

Rust error E0204: the trait Copy cannot be implemented for this type

Q: What does Rust error E0204 mean?

Copy is only allowed when every field is Copy too. A String, Vec or Box field makes the whole type non-Copy.

What it meansCopy is only allowed when every field is Copy too. A String, Vec or Box field makes the whole type non-Copy.

What rustc prints

error[E0204]: the trait `Copy` cannot be implemented for this type
 --> main.rs:5:15
  |
2 |     foo: Vec<u32>,
  |     ------------- this field does not implement `Copy`
...
5 | impl Copy for Foo { } // error!
  |               ^^^

Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.

Why it happens

#[derive(Copy, Clone)] on a struct with a String or Vec field.

How to fix it

1. Derive Clone only, and clone explicitly

#[derive(Clone)]
struct User { name: String }
let b = a.clone();

2. Or make the fields Copy

For example an id or a &'static str instead of a String.

#[derive(Clone, Copy)]
struct Id(u64);

Other wordings of this error

the trait Copy cannot be implemented for this type, this field does not implement `Copy`

E0204Types and traits

Activein rustc 1.99.0

8related errors linked below

The compiler team's explanation

The Copy trait was implemented on a type which contains a field that doesn't implement the Copy trait.

Erroneous code example:

struct Foo {
    foo: Vec<u32>,
}

impl Copy for Foo { } // error!

The Copy trait is implemented by default only on primitive types. If your type only contains primitive types, you'll be able to implement Copy on it. Otherwise, it won't be possible.

Here's another example that will fail:

#[derive(Copy)] // error!
struct Foo<'a> {
    ty: &'a mut bool,
}

This fails because &mut T is not Copy, even when T is Copy (this differs from the behavior for &T, which is always Copy).

From rustc --explain E0204 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.

Up next

Often hit nextE0308: mismatched typesA related error from the same family.Read it next →

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