1 You are trying to use an identifier that is either undefined or not a struct.
2 Erroneous code example:
6 let x = Foo { x: 1, y: 2 };
10 In this case, `Foo` is undefined, so it inherently isn't anything, and
11 definitely not a struct.
16 let x = foo { x: 1, y: 2 };
20 In this case, `foo` is defined, but is not a struct, so Rust can't use it as