CRDT datatype implementation

[vladimirmyshkovski]

Conflict-free replicated data type implementation

[spytheman]

Suggested change

	// inc_val allows passing in an arbitrary delta to increment the
	// increment_value allows passing in an arbitrary delta to increment the

[spytheman]

Suggested change

	// count returns the total count of this counter across all the
	// value returns the total count of this counter across all the

[spytheman]

Suggested change

	// Merge combines the counter values across multiple replicas.
	// merge combines the counter values across multiple replicas.

[spytheman]

Unless you want to test private functions, it is a little better, to not use module crdt for the test (i.e. just make a test that uses import datatypes.crdt, like a normal user program will have to) - the reason is that in this way, the test will also serve as an example, that is directly copy/paste-able.

[spytheman]

Suggested change

	main_set map[T]T
	main_set map[T]bool

For most types, like strings or pointers etc, sizeof(bool) < sizeof(T), and the map here is only used for its keys afaik.

[spytheman]

Suggested change

	mut elements := []T{}
	for _, element in g.main_set {
	elements << element
	}
	return elements
	return g.main_set.keys()

[spytheman]

Given if value in o.add_map { passed, then for uid, _ in o.add_map { is not needed - uid will be value.

It may be helpful to use some variation of key for the name of the parameter, instead of value, then the code below will be clearer.

[spytheman]

what does this do?

[spytheman]

this does not seem to have side effects too, what is the intent for it?

[spytheman]

Suggested change

	// Merge combines both the PN-Counters and saves the result
	// merge combines both the PN-Counters and saves the result

[medvednikov]

@vladimirmyshkovski can you please fix these issues, so that we can merge the PR?

[enghitalo]

From Wikipedia (good to update the doc)

The CRDT concept was formally defined in 2011 by Marc Shapiro, Nuno Preguiça, Carlos Baquero and Marek Zawirski.[9] Development was initially motivated by collaborative text editing and mobile computing. CRDTs have also been used in online chat systems, online gambling, and in the SoundCloud audio distribution platform. The NoSQL distributed databases Redis, Riak and Cosmos DB have CRDT data types.