Function union

union<T extends Record<string, CodecLike<any, any, any>>>(
    codecLayout: T,
    fields?: Record<keyof T, number | null | undefined>,
): Codec<
    UnionEncodable<T, keyof T>
    | { inner: UnionEncodable<T> },
    UnionDecoded<T, keyof T>,
    ChildContext<T>,
>
Constructs a union codec that can serialize and deserialize values tagged with a type identifier.

In accordance with the Molecule specification, union is always a dynamic-size type, regardless of whether its variants have identical fixed lengths.

If you need a fixed-size union type compatible with fixed containers like struct, array, or vector (as FixVec), use fixedUnion instead.

Serialization format:
1. 4-byte little-endian unsigned integer for the variant ItemId (tag).
2. Encoded bytes of the selected variant.
Type Parameters
- T extends Record<string, CodecLike<any, any, any>>
  A record mapping variant names to codecs.
Parameters
- codecLayout: T
  An object whose keys are variant names and values are codecs for each variant.
- Optionalfields: Record<keyof T, number | null | undefined>
  Optional mapping from variant names to custom numeric IDs. If omitted, the index of each variant in codecLayout is used as its ID.
Returns Codec<
    UnionEncodable<T, keyof T>
    | { inner: UnionEncodable<T> },
    UnionDecoded<T, keyof T>,
    ChildContext<T>,
>
Example
```
// Union without custom numeric IDs
union({ cafe: Uint8, bee: Uint16 });

// Union with custom numeric IDs
union({ cafe: Uint8, bee: Uint16 }, { cafe: 0xcafe, bee: 0xbee });

// Fixed-size union (explicit extension):
fixedUnion({ cafe: Uint16, bee: Uint16 });
```
- Defined in molecule/codec.ts:662

Function union

Type Parameters

Parameters

Returns Codec< UnionEncodable<T, keyof T> | { inner: UnionEncodable<T> }, UnionDecoded<T, keyof T>, ChildContext<T>,>

Example

Settings

Returns Codec<
UnionEncodable<T, keyof T>
| { inner: UnionEncodable<T> },
UnionDecoded<T, keyof T>,
ChildContext<T>,
>