| #### Note: this error code is no longer emitted by the compiler. |
| |
| You cannot define a struct (or enum) `Foo` that requires an instance of `Foo` |
| in order to make a new `Foo` value. This is because there would be no way a |
| first instance of `Foo` could be made to initialize another instance! |
| |
| Here's an example of a struct that has this problem: |
| |
| ``` |
| struct Foo { x: Box<Foo> } // error |
| ``` |
| |
| One fix is to use `Option`, like so: |
| |
| ``` |
| struct Foo { x: Option<Box<Foo>> } |
| ``` |
| |
| Now it's possible to create at least one instance of `Foo`: `Foo { x: None }`. |
