As suggested by Avi, we can return an actual mutation by moving it out of our
consumer. We will encapsulate it within an optional, to handle the cases where
the mutation cannot be found.
Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Reduces coupling. User's should not rely on the fact that it's an
std::map<>. It also allows us to extend row's interface with
domain-specific methods, which are a lot easier to discover than free
functions.
Ensure that read-side accessors are const. This is important in preparation
for multiple memtables (and later, sstables) since a read-side
mutation_partition may be a temporary object coming from multiple memtables
(and sstables) while a write-side mutation_partition is guaranteed to belong
to a single memtable (and thus, not be temporary).
Since writers will want non-const mutation_partitions to write to, they won't
be able to use the read-side accessors by accident.
Partitions should be ordered using Origin's ordering, which is first
by token, then by Origin's representation of the key. That is the
natural ordering of decorated_key.
This also changes mutation class to hold decorated_key, to avoid
decoration overhead at different layers.
