collection

# `gno.land/p/moul/collection/v3`

A generic collection with multiple indexes (unique, case-insensitive, sparse,
multi-value), backed by a **B+ tree** ([`gno.land/p/nt/bptree/v0`](https://github.com/gnolang/gno/tree/master/examples/gno.land/p/nt/bptree)).

It is the B+ tree successor to [`gno.land/p/moul/collection/v2`](../v2), which is
backed by an AVL tree. The exported API is identical to v2; only the on-chain
storage layout changed (hence the version bump — a compatibility change, not a
source change). A B+ tree packs many entries per persisted node, so each index
entry costs materially less storage and gas than the AVL backing. Prefer v3 when
the collection is part of persisted realm state.

Two operational caveats inherited from the in-place-mutating B+ tree backing:

- do **not** mutate the collection (`Set`/`Update`/`Delete`) from inside an index
  iteration callback — the AVL backing's copy-on-write tolerated it, this one does
  not;
- do **not** copy a non-zero `Collection` by value — the copies would share live
  tree nodes while their state diverges.

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Part of **[moul/gno-contracts](https://github.com/moul/gno-contracts)** — moul's versioned gno.land contracts. See the repository for the full catalog, build/test tooling, and usage.

**Dependency graph:**

![gno.land/p/moul/collection/v3 dependency graph](https://raw.githubusercontent.com/moul/gno-contracts/main/_assets/gno.land/p/moul/collection/v3/deps.png)

> ⚠️ **Disclaimer:** provided as-is, without warranty; not security-audited. Full disclaimer: [DISCLAIMER](https://github.com/moul/gno-contracts/blob/main/DISCLAIMER.md).

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