partialUpdate()

template<typename Key, typename Value, typename UpdateTag>

template<typename UpdateValue>

std::function< void(const UpdateValue &)> DataStorm::SingleKeyWriter< Key, Value, UpdateTag >::partialUpdate ( const UpdateTag & tag )

nodiscard

Gets a partial update generator function for the given partial update tag.

When called, the returned function generates a SampleEvent::PartialUpdate sample with the given partial update value. The UpdateValue template parameter must match the UpdateValue type used to register the updater with the Topic::setUpdater method. A partial update resolves against the key's current value, so the key must have a current value when the returned function is called: a full value was written for the key and the key was not since removed. Calling the returned function for a key with no current value is an application error that throws std::logic_error and publishes nothing. A reader that uses a sample filter receives only the samples its filter matches: such a reader can lack a current value for the key even though the writer has one, and it discards partial updates until it receives a full value for the key. See Topic::setSampleFilter.

Parameters

tag	The partial update tag.

Definition at line 1429 of file DataStorm.h.