---
title: swift-primitives/swift-standard-library-extensions
framework: Swift Package Catalog
role: article
path: packages/swift-primitives/swift-standard-library-extensions
---

# swift-primitives/swift-standard-library-extensions

Targeted extensions to the Swift standard library: typed-throws overloads for closure-based stdlib APIs, result-builder DSLs for the standard collection types, safe-indexing accessors, and a pre-Swift-6.4-compiler `nonisolated(nonsending)` compatibility overload of `withTaskCance

## Quick Start

Pin to a version range and import:

```swift import Standard_Library_Extensions ```

### Typed throws across stdlib closures

The standard library's closure-based APIs (`withUnsafeBufferPointer`, `withUnsafeBytes`, `withUnsafePointer`, `withUnsafeTemporaryAllocation`, `Span.withUnsafeBufferPointer`, `Array.withUnsafeBufferPointer`, …) are declared `rethrows`, which erases the closure's typed error. This package adds parallel overloads that preserve `throws(E)`:

```swift enum ParseError: Error { case invalid }

let bytes: [UInt8] = [0x48, 0x65, 0x6c] let first: UInt8 = try bytes.withUnsafeBufferPointer { buffer throws(ParseError) in     guard buffer.count > 0 else { throw .invalid }     return buffer[0] } // Error type ParseError is preserved at the call site. ```

Without this package, the `throws(ParseError)` constraint is lost the moment the closure crosses a `rethrows` boundary.

### Declarative collection construction with control flow

Result-builder DSLs are provided for `Array`, `ArraySlice`, `ContiguousArray`, `Set`, `Dictionary`, `CollectionOfOne`, `Optional`, `Range`, `ClosedRange`, `Bool`, `Result`, `String`, and `Substring`:

```swift let numbers = Array {     1     2     if includeThree {         3     }     for n in 4...6 {         n     } } // Builds the array declaratively without intermediate `+` concatenations. ```

### Safe indexing

```swift let xs = [10, 20, 30] xs[safe: 1..<2]    // Optional(ArraySlice([20])) xs[safe: 5..<10]   // nil — out of bounds, no crash xs[safe: -1..<2]   // nil — invalid range, no crash ```

### `nonisolated(nonsending)` cancellation handler

Before the Swift 6.4 compiler, the standard library's `withTaskCancellationHandler` is not `nonisolated(nonsending)`, which can introduce executor hops. On those compilers, this package's compatibility overload preserves the caller's isolation context. Swift 6.4 and later compilers use the standard library's equivalent overload directly:

```swift let result = try await withTaskCancellationHandler {     try await someOperation() } onCancel: {     cancelExternalResource() } // No unnecessary suspension at the operation boundary. ```

## Installation

Add to your `Package.swift`:

```swift dependencies: [     .package(         url: "https://github.com/swift-primitives/swift-standard-library-extensions.git",         from: "0.1.0"     ), ] ```

Then add the target dependency:

```swift .target(     name: "YourTarget",     dependencies: [         .product(name: "Standard Library Extensions", package: "swift-standard-library-extensions"),     ] ) ```

## Architecture

The package ships two targets:

| Target | Role | |--------|------| | `Standard Library Extensions` | Main target — extensions and overloads. | | `Standard Library Extensions Test Support` | Test-support shell for downstream packages that wish to import test fixtures. |

Source files follow one type per file; nested types use the Type.NestedType.swift naming pattern (e.g., `Array.Builder.swift`, `Result.Builder.swift`).

## Platform Support

The package is `nonisolated(nonsending)`-aware and uses Swift 6 language features: typed throws (`throws(E)`), `~Copyable`, `~Escapable`, `LifetimeDependence`, and `SuppressedAssociatedTypes`. Built against Swift 6.3 (stable) and Swift 6.4-dev (nightly).

| Platform | Minimum | |----------|---------| | macOS | 26.0 | | iOS | 26.0 | | tvOS | 26.0 | | watchOS | 26.0 | | visionOS | 26.0 | | Linux | Swift 6.3 | | Embedded Swift | Swift 6.4-dev |

## Stability

Pre-1.0. APIs are still evolving and may change between minor versions until 1.0.0 is tagged. Within the 0.x.y line, `0.<major>.0` releases may carry breaking changes; `0.<major>.<patch>` releases are additive only.

## License

Apache License 2.0 — see [LICENSE.md](./LICENSE.md).

## Package Metadata

Repository: swift-primitives/swift-standard-library-extensions

Default branch: main

README: README.md