src/util/stableindex.jl

`Base.haskey`

Whether an ID is in use.

`Base.length`

Total number of IDs in use.

`Base.getindex`

Get index at ID.

`Base.setindex!`

Map ID to a new index. The ID must be in use.

`Base.push!`

Add a new index. Returns its ID.

`Base.delete!`

Remove a recorded index at ID.

`Base.empty!`

Clear all index records.

`Base.iterate`

Iterates through valid IDs in the StableIndex.