# Collection Helpers Review

## Scope

- Issue: #20
- Baseline: `origin/develop` at `2998bc9`
- Reviewed diff: `crates/collections` helper implementation plus research note

## Evidence

- `bluetape4k-core` source review: `CollectionSupport.kt`, `IterableSupport.kt`, `SequenceSupport.kt`, `ListSupport.kt`, `IteratorSupport.kt`, `MapEntrySupport.kt`, `PaginatedList.kt`
- Rust API review: helpers limited to gaps not directly covered by Rust 1.85 standard iterator/slice/map APIs
- Follow-up split: #32 for slice/list boundary helpers, #33 for pagination value types
- `git diff --check`: PASS
- `cargo fmt --all --check`: PASS
- `cargo test -p bluetape-rs-collections`: PASS, 15 unit tests and 10 doctests
- `cargo test --workspace --all-features`: PASS
- `cargo clippy --workspace --all-targets --all-features -- -D warnings`: PASS
- `RUSTDOCFLAGS='-D warnings' cargo doc --workspace --no-deps`: PASS

## Findings

- P0: none
- P1: none
- P2: none
- P3: none

## 7-Tier Review

| Tier | Result | Evidence |
| --- | --- | --- |
| API contract | PASS | Rust-native free functions, explicit `Result`, no Kotlin extension-style mechanical port |
| Correctness | PASS | chunk/window/group/frequency/map/result behavior covered by tests |
| Error handling | PASS | invalid sizes return `CollectionError::InvalidSize`; fallible map preserves caller error type |
| Standard-library overlap | PASS | slice `chunks/windows`, range collect, `Vec` mutation, and primitive conversion wrappers excluded |
| Docs | PASS | Rustdoc examples pass as doctests |
| Scope control | PASS | larger pagination and slice/list policy helpers split into #32 and #33 |
| Validation | PASS | fmt, tests, clippy, rustdoc warning gate passed |

## Gate

P0=0 P1=0

Verdict: PASS. The API is Rust-native, avoids direct Kotlin/JVM porting, documents allocation/error behavior, and includes success, grouping, empty/boundary, and error-path tests.
