# `Dllb.MetaAST.Similarity`
[🔗](https://github.com/Oeditus/dllb_ex/blob/v0.9.0/lib/dllb/meta_ast/similarity.ex#L1)

Structural similarity comparison for MetaAST trees.

Provides functions for comparing AST subtrees structurally (ignoring
names and values), computing structural fingerprints for fast
pre-filtering, and detecting code clones across a set of subtrees.

Mirrors the Rust `dllb-code-intel::similarity` module, enabling
client-side clone detection without a server round-trip.

## Usage

    sim = Dllb.MetaAST.Similarity.structural_similarity(tree_a, tree_b)
    # => 0.95

    clones = Dllb.MetaAST.Similarity.find_clones(trees, threshold: 0.8)
    # => [%{index_a: 0, index_b: 3, similarity: 0.92}, ...]

# `find_clones`

```elixir
@spec find_clones(
  [tuple()],
  keyword()
) :: [map()]
```

Find pairs of subtrees with structural similarity above the given threshold.

Uses fingerprints for fast pre-filtering: only pairs whose root hash matches
(or that have >50% fingerprint overlap) are subjected to full comparison.

## Options

  * `:threshold` - minimum similarity (default 0.8)

Returns a list of `%{index_a: i, index_b: j, similarity: score}` maps,
sorted by descending similarity.

# `structural_similarity`

```elixir
@spec structural_similarity(tuple(), tuple()) :: float()
```

Compute structural similarity between two MetaAST subtrees.

Returns a score in `0.0..1.0` comparing tree shape and node types,
ignoring names, values, and metadata. Uses greedy best-match pairing
of children weighted by subtree size.

- Same node type, both leaves: 1.0
- Same node type, both composite: recursive greedy child matching
- Different node type: 0.0 base, with partial credit if children overlap

# `subtree_hash`

```elixir
@spec subtree_hash(tuple()) :: non_neg_integer()
```

Compute a single hash of the entire subtree structure.

Two structurally identical trees (same node types, same arity at each
position) produce the same hash.

# `tree_fingerprint`

```elixir
@spec tree_fingerprint(tuple()) :: [non_neg_integer()]
```

Produce a structural fingerprint of a MetaAST tree.

Returns a list of integer hashes representing the structural skeleton
(node types + arity at each level). Useful for fast pre-filtering before
expensive similarity comparison.

---

*Consult [api-reference.md](api-reference.md) for complete listing*