# Adopt Parity and Consistency as Principles For `go-cuckoo`

**Status**: Accepted

## Context

I built `go-cuckoo`'s API interface without design intent.
Up until now, I paid more attention implementing the underlying functionality of the cuckoo hashing.
With the fundamentals of the algorithm built, I should revisit the interface.

The goal of this project was to create an implementation of cuckoo hashing, while adhering to Go's idioms, and being as usable as possible.
While the implementation does work, it lacks direction.

## Decision

To resolve this, I'm enforcing two new principles onto the contract of `go-cuckoo`:

- **Parity (with `map`)**:
  A `go-cuckoo` table should have the same core functionality as `map`.
  By 'core', I mean `map`'s built-in syntax and functions (e.g. `range`, `m[k]`), and the `maps` package.
  Higher parity means users can trust that `go-cuckoo` can do what `map` can do.

- **Consistency (with `map`)**:
  A `go-cuckoo` table should behave similarly to `map`, so users will intuitively know how to use it.
  Higher consistency lowers the cognitive load users must carry.

While these principles should guide the interface of `go-cuckoo`, they should not be absolute.
The behavior of `go-cuckoo` is distinct from `map` (e.g. `Put` can fail; see `ErrBadHash`), so do not equate them.

## Consequences

1. The repository should contain a living document, describing the interface differences between `go-cuckoo` and `map`.
   I should prioritize limiting any disparity.
   (I already started work on branch `docs/interface-congruency-analysis`.)
   - [ ] Produce the first draft to uncover any current disparity.
   - [ ] Link the document to the `README.md`.
2. Analyze the consistency of `go-cuckoo`'s current interface.
   Unlike the analysis of parity, this should be a one time document.
   Consistency is implicit to users, and does not need to be referenced.
   But, any rationale should be documented in commit messages, or future ADRs.
   - [ ] Produce the analysis document.
   - [ ] Resolve any issues found.
3. The repository should support both design principles.
   As I resolve gaps in parity and consistency, I should feed any reusable heuristics back into the contributing guide.
   - [ ] State these principles in the `README.md` and `doc.go`.
   - [ ] Ground the contributing guide and pull request template in these new principles.