An enum models a value selected from mutually exclusive variants. Unlike a struct, which contains all its fields, an enum contains only its active variant. Variants may be unit-like, tuple-like, struct-like, or carry named or anonymous types. section 4.5.4
Use enums to:
- Represent a closed set of named choices, including C-like values with explicit discriminants. section 4.5.4
- Attach data directly to each choice through tuple, struct, or anonymous variant types. section 4.5.4
- Add debugging output with derived traits such as Debug, or implement conversions manually when automatic conversion is unavailable. section 4.5.4 section 4.9
enum EnumTypes {
NamedType, #1
String, #2
NamedString(String), #3
StructLike { name: String }, #4
TupleLike(String, i32), #5
}
Compare unit-like, named-data, tuple-like, and struct-like variants in one compact declaration. section 4.5.4
Conversion and discriminants
A C-like enum can be cast to u32 for comparison or output when its variants are enumerated. The reverse conversion is not automatic: implement From<u32> manually, match every known discriminant, and decide how unknown values should be handled. The demonstrated implementation panics for an unknown value, so production code should treat that failure policy as an explicit design choice. section 4.5.4
Prefer data-carrying variants when the choice and its payload belong together. Derive standard traits where sufficient, and avoid assuming that an enum's numeric discriminant provides a general-purpose serialization or conversion contract. section 4.5.4 section 4.9
