Rust errors / Types and traits
Rust compiler error · checked with rustc 1.99.0
Rust error E0720: cannot resolve opaque type
What it meansAn impl Trait type expands to a recursive type.
What rustc prints
error[E0720]: cannot resolve opaque type
--> main.rs:1:29
|
1 | fn make_recursive_type() -> impl Sized {
| ^^^^^^^^^^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.
E0720Types and traits
Activein rustc 1.99.0
8related errors linked below
The compiler team's explanation
An impl Trait type expands to a recursive type.
Erroneous code example:
fn make_recursive_type() -> impl Sized {
[make_recursive_type(), make_recursive_type()]
}An impl Trait type must be expandable to a concrete type that contains no impl Trait types. For example the previous example tries to create an impl Trait type T that is equal to [T, T].
From rustc --explain E0720 (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
- E0715impls for marker traits cannot contain items
- E0719the value of the associated type `Item` in trait `Iterator` is already specified
- E0735generic parameters cannot use `Self` in their defaults
- E0737`#[track_caller]` can only be used with the Rust ABI
Up next
Often hit nextE0308: mismatched typesA related error from the same family.Read it next →Did this answer your question?