Available on crate features assistant-service or conversational-search-service or recommendation-service or search-service or serving-config-service or user-event-service only.
Non-exhaustive structs could have additional fields added in future. Therefore, non-exhaustive structs cannot be constructed in external crates using the traditional Struct { .. } syntax; cannot be matched against without a wildcard ..; and struct update syntax will not work.
Highly recommended for logged-in users. Unique identifier for logged-in
user, such as a user name. Don’t set for anonymous users.
Always use a hashed value for this ID.
Don’t set the field to the same fixed ID for different users. This mixes
the event history of those users together, which results in degraded
model quality.
The field must be a UTF-8 encoded string with a length limit of 128
characters. Otherwise, an INVALID_ARGUMENT error is returned.