The repeated oneof construct in Protocol Buffers is used when we want to define a field that can contain multiple values, but only one value can be set at a time. This is useful in situations where we need to represent a choice between multiple options.
Let’s consider an example to understand it better. Suppose we have a message type called Contact with a field called phone_numbers. We want to indicate that each contact can have multiple phone numbers, but only one of them can be considered as the primary number. The repeated oneof construct can help us achieve that.
message Contact {
repeated string phone_numbers = 1;
oneof primary_phone {
string primary_number = 2;
}
}
In the above example, the phone_numbers field is defined as repeated, indicating that it can have zero or more values. The primary_phone oneof block contains the primary_number field, which is a string representing the primary phone number for the contact.
Now, let’s assume we have a contact with multiple phone numbers:
Contact myContact = {
phone_numbers: ["123", "456", "789"],
primary_number: "456"
};
In the above example, the phone_numbers field contains three phone numbers. However, the primary_number field is set to “456”, indicating that it is the primary phone number.
By using the repeated oneof construct, we can ensure that only one value is set within the oneof block, providing a clear indication of the choice between multiple options.