Standard Library

The Swift standard library provides the runtime behaviour for all built-in types and protocols. tswift implements these entirely in Rust inside tswift-std.

The frontend provides type shapes; tswift-std provides the behaviour.

Legend: ✅ Done · 🟡 Partial · ⬜ Todo

Overall coverage

Standard Library73% (19/26)

Core Value Types

Core value types75% (6/8)
Status Type Notes
✅ Int, UInt family (all widths) Overflow-trapping + &+/&-/&* wrapping
✅ Float, Double IEEE 754, math functions
✅ Bool
🟡 String (UTF-8, NFC, views) + Character Most APIs work; CharacterView, UnicodeScalarView partial
🟡 Substring Slicing works; full index arithmetic incomplete
✅ Optional<Wrapped> Full — binding, chaining, coalescing, patterns
✅ Range / ClosedRange / Stride For-in, contains, count, overlaps
⬜ Tuples as first-class stdlib types Runtime supports tuples; stdlib protocols not wired

Collections

Collections80% (4/5)
Status Type Notes
✅ Array<Element> + CoW append, insert, remove, sorted, map/filter/reduce, slicing
✅ Dictionary<Key,Value> + CoW keys, values, merging, filter, mapValues
✅ Set<Element> + CoW union, intersection, subtracting, symmetricDifference
✅ ContiguousArray / ArraySlice Backed by Array in the runtime
⬜ isKnownUniquelyReferenced CoW correctness helper — not exposed

Protocols That Drive the Language

Key protocols70% (7/10)
Status Protocol Notes
✅ Equatable / Hashable / Comparable Synthesised for structs/enums with synthesised conformance
✅ Sequence / IteratorProtocol Custom sequences via makeIterator()
⬜ Collection / BidirectionalCollection / RandomAccessCollection Index arithmetic not yet fully implemented
⬜ RangeReplaceableCollection
✅ ExpressibleBy*Literal All literal-conversion protocols
✅ CustomStringConvertible / CustomDebugStringConvertible
✅ RawRepresentable / CaseIterable Enum conformances synthesised
✅ Codable / Encodable / Decodable JSON encode/decode via synthesised CodingKeys
✅ Identifiable
⬜ Sendable Accepted by parser; not statically checked
⬜ AsyncSequence / AsyncIteratorProtocol for await works; custom AsyncSequence conformances partial

Free Functions & Utilities

Free functions86% (6/7)
Status API Notes
✅ print / debugPrint / dump Streaming to stdout
✅ map/filter/reduce/flatMap/compactMap/sorted/zip All HOF on sequences
✅ assert/precondition/fatalError/assertionFailure Trapping semantics
✅ min/max/abs/stride/zip/swap
✅ Result<Success, Failure> Both cases, map, flatMap, mapError
✅ MemoryLayout<T> size, stride, alignment
⬜ Unsafe*Pointer family Requires unsafe Rust; out of scope for now

What’s next

The highest-impact missing pieces:

  1. Collection protocol conformances — needed for custom types to slot into for-in, count, first, last, index subscripting.
  2. String index arithmetic — String.Index, index(before:), index(after:), index(_:offsetBy:) needed for full character-level manipulation.
  3. AsyncSequence — needed to implement for await over custom types.

To see how these map to GitHub issues, visit the issue tracker.