| A closure or generator was constructed that references its own type. |
| |
| Erroneous code example: |
| |
| ```compile_fail,E0644 |
| 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*. |
