Rust errors / Types and traits
Rust compiler error · checked with rustc 1.99.0
Rust error E0562: `impl Trait` is not allowed in the type of variable bindings
What it meansimpl Trait is only allowed as a function return and argument type.
What rustc prints
error[E0562]: `impl Trait` is not allowed in the type of variable bindings --> main.rs:2:23 | 2 | let count_to_ten: impl Iterator<Item=usize> = 0..10; | ^^^^^^^^^^^^^^^^^^^^^^^^^ | = note: `impl Trait` is only allowed in arguments and return types of functions and methods = note: see issue #63065 <https://github.com/rust-lang/rust/issues/63065> for more information
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.
E0562Types and traits
Activein rustc 1.99.0
8related errors linked below
The compiler team's explanation
impl Trait is only allowed as a function return and argument type.
Erroneous code example:
fn main() {
let count_to_ten: impl Iterator<Item=usize> = 0..10;
// error: `impl Trait` not allowed outside of function and inherent method
// return types
for i in count_to_ten {
println!("{}", i);
}
}Make sure impl Trait appears in a function signature.
fn count_to_n(n: usize) -> impl Iterator<Item=usize> {
0..n
}
fn main() {
for i in count_to_n(10) { // ok!
println!("{}", i);
}
}See the reference for more details on impl Trait.
From rustc --explain E0562 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.
Related errors
- E0308mismatched types
- E0277the trait bound is not satisfied
- E0599no method named X found in the current scope
- E0433failed to resolve
- E0531cannot find tuple struct or tuple variant `Type` in this scope
- E0561patterns aren't allowed in function pointer types
- E0567auto traits cannot have generic parameters
- E0569requires an `unsafe impl` declaration due to `#[may_dangle]` attribute
Up next
Often hit nextE0308: mismatched typesA related error from the same family.Read it next →Did this answer your question?