Mastering Rust - Second Edition

Enums

When you need to model something that can be of different kinds, enums are the way to go. They are created using the enum keyword, followed by the name of the enum, followed by a pair of braces. Within braces, we can write all the possibilities of the type, which are called variants. These variants can be defined with or without data contained in them, and the data contained can be any primitive type, structs, tuple structs, or even an enum. However, in the recursive case, where you have an enum, Foo, and also a variant which holds Foo, the variant needs to be behind a pointer (Box, Rc, and so on) type to avoid having recursively infinite type definitions. Because enums can also be created on the stack, they need to have a predetermined ...