1.6.2 Aggregation

It is possible to specify homogeneous vectors of things (e.g. lists of numbers) using the repeated attribute. You specify a repeated field as follows:

    repeated(22, float([1,2,3,4])),
    repeated(23, enum(tank_state([empty, half_full, full]))).

The first clause above, will cause all four items in the list to be encoded in the wire-stream as IEEE-754 32-bit floating point numbers, all with tag 22. The decoder will aggregate all items in the wire-stream with tag 22 into a list as above. Likewise, the all items listed in the second clause will be encoded in the wire-stream according to the mapping defined in an enumeration (described below) tank_state/2, each with tag 23.

Notes:

Beware that there is no explicit means to encode an empty set. The protobuf specification provides that a repeated field may match a tag zero or more times. The empty set, while legal, produces no output on encode. While decoding a repeated term, failure to match the specified tag will yield an empty set of the specified host type.

The protobuf grammar provides a variant of the repeated field known as "packed." Packed, repeated fields are currently not supported by our interpreter.