Rust errors / Types and traits
Rust compiler error · checked with rustc 1.99.0
Rust error E0644: closure/coroutine type that references itself
What it meansA closure or generator was constructed that references its own type.
What rustc prints
error[E0644]: closure/coroutine type that references itself --> main.rs:8:10 | 8 | fix(&|y| { | ^^^ recursive type with infinite-size name | = note: closures cannot capture themselves or take themselves as argument; this error may be the result of a recent compiler bug-fix, see issue #46062 <https://github.com/rust-lang/rust/issues/46062> for more information note: required by a bound in `fix` --> main.rs:2:12 | 1 | fn fix<F>(f: &F) | --- required by a bound in this function 2 | where F: Fn(&F) | ^^^^^^ required by this bound in `fix`
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.
The compiler team's explanation
A closure or generator was constructed that references its own type.
Erroneous code example:
fn fix<F>(f: &F)
where F: Fn(&F)
{
f(&f);
}
fn main() {
fix(&|y| {
// Here, when `x` is called, the parameter `y` is equal to `x`.
});
}Rust does not permit a closure to directly reference its own type, either through an argument (as in the example above) or by capturing itself through its environment. This restriction helps keep closure inference tractable.
The easiest fix is to rewrite your closure into a top-level function, or into a method. In some cases, you may also be able to have your closure call itself by capturing a &Fn() object or fn() pointer that refers to itself. That is permitting, since the closure would be invoking itself via a virtual call, and hence does not directly reference its own *type*.
From rustc --explain E0644 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.
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- E0643method `foo` has incompatible signature for trait
- E0665`#[derive(Default)]` on enum with no `#[default]`
- E0666nested `impl Trait` is not allowed
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