Enums

An enum is an integer on the wire with a name for each meaningful value. It corresponds to a Rust enum with the same discriminants. The generated Rust type is #[repr(uN)] where N is the backing width.

Closed enums

message_type = enum {
    Request = 1,
    Response = 2,
    Error = 3,
}

This emits a MessageType Rust enum. Values must be distinct and fit the inferred backing width.

Parsing. Reads the backing integer and maps it to a variant. Any other value is a parse error.

Preparation and serialization. Preparation always succeeds and reports the backing width. Serialization writes the variant’s discriminant as the backing integer.

Open enums

Add ... after the variants to preserve unknown values:

message_type = enum {
    Request = 1,
    Response = 2,
    ...
}

Parsing. A recognised value maps to its variant, and anything else is kept as Unknown(value).

Preparation and serialization. Same width as the closed form. Known variants serialize as before; Unknown(value) serializes as value.

Choosing the backing width

The backing width is what actually determines how many bytes appear on the wire. Without a suffix, Vest selects the smallest unsigned width containing every value. A suffix on any enumerator fixes the type; all supplied suffixes must agree:

wide_type = enum {
    Request = 1u16,
    Response = 2,
}

The supported executable backing widths are u8, u16, u24, u32, and u64.

Inside a bits block, a suffix such as 0u3 instead selects a three-bit enum. See Bit fields.