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