Wrapper for domains. (`BitVector` / `StateSparseSet`)

[Whebon]

Holes can have domains of two different types:

• StateSparseSet (for stateful holes)
• BitVector (for all other holes)

Propagators can use domain functions to check certain properties. For example:

• findfirst, to get the smallest/minimum value of the domain
• sum, to get the number of rules in the domain

These functions are used as if the domain was a BitVector. However, they are not intuitive for what they are supposed to do. For a StateSparseSet this is even more confusing, because sum seems like it should behave completely different.

Solution

Use a wrapper function around domains and give intuitive names to domain operations. (Like minimum and size)

abstract type AbstractDomain end

struct BitVetorDomain
    domain::BitVector
end

struct StateDomain
    domain::StateSparseSet
end

It should support at least the following operations:

• Base.minimum(::AbstractDomain). return the lowest rule index.
• Base.maximum(::AbstractDomain). return the highest rule index.
• Base.iterate(::AbstractDomain). iterate over all rules in the domain.
• Base.size(::AbstractDomain). return the number of rules in the domain.
• Base.in(::AbstractDomain). check if a rule is in the domain.
• Base.findall(::AbstractDomain). return all rules in the domain.
• Base.isempty(::AbstractDomain). check if the domain is empty.
• remove!(::AbstractDomain, rule::Int). remove a rule from the domain.
• remove_all_but!(::AbstractDomain, rule::Int). remove all but a single rule from the domain.
• remove_below!(::AbstractDomain, rule::Int) remove all remove with a lower rule index from the domain.
• remove_above!(::AbstractDomain, rule::Int) remove all remove with a higher rule index from the domain.
• are_disjoint(::AbstractDomain, ::AbstractDomain) return true if two domains have an empty intersection.
• get_intersection(::AbstractDomain, ::AbstractDomain) returns rules that are in both domains.
• is_subdomain(sub::AbstractDomain, dom::AbstractDomain) check if sub sub-domain of dom.

Why is this not here yet

Adding the wrapper might cause overhead when copying over many holes during program iteration.