kofre.dotted

The context describes dots that have been seen. The store describes which value is associated for a given dot. Dots that are removed from the store are considered deleted. All others are merged as for normal maps.

The delta CRDT paper calls this a DotFun

DotMap is a dot store implementation that maps keys of an arbitrary type K to values of a dot store type V. See ObserveRemoveMap for a usage example.

Implicit aliases in companion object for search path

DecomposableDotStore is the typeclass trait for dot stores, data structures that are part of causal CRDTs and make use of dots to track time.

The delta CRDT paper introduces a lot of individual abstractions that all do a lot of cool stuff, but often not separated into their pieces. This is one of those pieces systematically handling removals based on metadata.

The context encodes dots that have been seen. The store of type A is assumed to be something that stores individual information per dot. We represent removals as context that contains a dot, but a store that no longer contains the dot. Thus, when merging the abstract logic is somewhat along the lines of: Both contain the (dot, value) pair? => merge value recursively. Only one contains the dot in the context? => keep that value. Both contain the dot, but at least one has no matching value? => remove all values for that dot.

Separating into a mergePartial allows extracting the context into the outermost layer reducing metadata overhead.

See: Dot stores in delta state replicated data types

But here, a dot store is something that can be seen as a Dots