Constructed types

Slice provides three built-in generic types: Dictionary<Key, Value>, Result<Success, Failure>, and Sequence<T>. You need to specify the type argument(s) of such a generic type in order to get an actual type - a constructed type. This page describes the encoding of such constructed types.

Dictionary

A dictionary with N entries is encoded like a sequence with N elements where the element type is a compact struct:

compact struct Pair { key: Key, value: Value }

Key represents the dictionary's key type and Value represents the dictionary's value type.

Result

A Result<Success, Failure> is encoded exactly like a compact variant enum with two variants (Success and Failure), where each variant has a single field of the respective type (Success or Failure).

For example, a Result<string, int32> is encoded like a:

compact enum StringInt32Result {
    Success(value: string)
    Failure(value: int32)
}

Sequence with a non-optional element type

A sequence of N elements with a non-optional element type T is encoded as a varuint62-encoded N followed by each element encoded in order.

Example: empty sequence

An empty sequence is encoded as:

0x00: size 0

Example: sequence of int32

A sequence of int32 with values 5, 32 and 9 is encoded as:

0x0C:                3 elements (varuint62 on 1 byte)
0x05 0x00 0x00 0x00: 5 over 4 bytes in little-endian order
0x20 0x00 0x00 0x00: 32 over 4 bytes in little-endian order
0x09 0x00 0x00 0x00: 9 over 4 bytes in little-endian order

Sequence with an optional element type

A sequence of N elements with a optional element type T? is encoded as a varuint62-encoded N followed by a bit sequence with N bits, followed by each element with a value encoded in order.

Example: sequence of int32?

A sequence of int32? with values 5, no-value, 9 and no-value is encoded as:

0x10:                4 elements (varuint62 on 1 byte)
0b00000101:          bit sequence with positions 0 and 2 set
0x05 0x00 0x00 0x00: 5 over 4 bytes in little-endian order
0x09 0x00 0x00 0x00: 9 over 4 bytes in little-endian order