Using collections in Protobuf
Protobuf supports two types of collections: repeated fields and maps. Repeated fields are analogous to arrays or lists in C#. They represent a collection of singular objects. Maps are analogous to dictionaries in C#. They represent a collection of key-value pairs.
Repeated field collections can contain any data type, but you cannot use additional keywords inside of them. For example, you cannot have an equivalent of a multi-dimensional array by having a repeated keyword inside a repeated field.
Map fields can use any data type as a value, but its key needs to be either any of the integer types or a string. It cannot be a bytes, enum, float, or double data type, or any custom message type. Neither its key, its value, nor the whole field itself can be repeated. Let's discuss each type further in the next subsections.
Repeated fields
Inside the greet.proto file, add the following fields to the NestedMessage definition:
repeated string...