Contents

21-dot-dev/swift-boost

Vendored Boost 1.90.0 C++ header-only modules for Swift packages. Uses Swift's C++ interoperability to make Boost headers available to Swift targets.

Why swift-boost?

Reach for swift-boost when you need a wide cross-section of header-only Boost in a SwiftPM-native form across Apple platforms and Linux — for example, Bitcoin Core ports like swift-bitcoin that consume multi_index, signals2, mp11, and dozens of other modules. The 37 modules ship as individual library products plus a boost umbrella, so you don't have to subtree Boost into your own package or hand-write per-module SPM wiring.

Don't reach for it if you only need one or two header-only Boost modules — subtree-ing them directly into your own package is simpler and avoids taking a dependency. And if your goal is portable C++ standard-library functionality, modern C++17/20 (std::variant, std::optional, std::filesystem) covers a lot of what Boost historically provided without any vendored dependency.

Contents

Features

  • 37 Boost modules as individual SwiftPM library products, plus a boost umbrella product mirroring upstream Boost's CMake Boost::headers target
  • Swift/C++ interop ready — pair with a C++ bridging header to call Boost from Swift via interoperabilityMode(.Cxx)
  • Apple platforms + Linux — macOS 13+, iOS, visionOS, and Ubuntu 22.04+ (Swift 6.1+, C++17)
  • Header-only — no Boost source compilation; ships only public headers
  • Linux-native modulemaps — ships requires !cplusplus modulemap stubs so consumers don't need post-resolve workarounds for Swift's -fno-implicit-modules default

Available Modules

Each Boost module is exposed as an individual SwiftPM library product.

| Category | Modules | |----------|--------| | Algorithms & Ranges | algorithm, foreach, iterator, range | | Containers | array, container, multi_index, variant, optional, tuple | | Memory & Pointers | smart_ptr, move | | Metaprogramming | mp11, mpl, preprocessor, type_traits, type_index | | Serialization & I/O | serialization, lexical_cast, io | | Signals & Events | signals2 | | Utilities | bind, config, core, describe, function, utility |

See Package.swift for the complete list of all 37 modules.

A boost umbrella product is also available, mirroring upstream Boost's CMake Boost::headers target. Depending on boost brings in every module's headers transitively, which is convenient for consumers (such as Bitcoin Core ports) that use a wide cross-section of Boost.

Installation

This package uses Swift Package Manager.

Using Xcode

  1. Go to File > Add Packages...
  2. Enter the package URL: https://github.com/21-DOT-DEV/swift-boost
  3. Select the desired version (recommend pinning to an exact version — see Versioning)

Using Package.swift (Recommended)

Add the following to your Package.swift:

.package(url: "https://github.com/21-DOT-DEV/swift-boost.git", exact: "1.90.0"),

[!NOTE] swift-boost tags mirror upstream Boost releases. Pin with exact: because Boost minor releases can deprecate or remove modules. See Versioning below.

Then add the Boost modules you need as dependencies and enable C++ interop on the consuming target:

.target(
    name: "MyTarget",
    dependencies: [
        .product(name: "algorithm", package: "swift-boost"),
        .product(name: "optional", package: "swift-boost"),
    ],
    swiftSettings: [
        .interoperabilityMode(.Cxx),
    ]
),

For consumers using a wide cross-section of Boost, depend on the umbrella product instead:

.target(
    name: "MyTarget",
    dependencies: [
        .product(name: "boost", package: "swift-boost"),
    ],
    swiftSettings: [
        .interoperabilityMode(.Cxx),
    ]
),

Set cxxLanguageStandard: .cxx17 (or higher) at the package level.

Versioning

swift-boost tags mirror upstream Boost releases. Recent tags:

| Tag | Boost upstream | |---|---| | 1.90.0 | Boost 1.90.0 | | 1.81.0 | Boost 1.81.0 | | 1.80.0 | Boost 1.80.0 |

[!NOTE] Boost minor releases can deprecate or remove modules. Pin consumers with exact: so you choose explicitly when to take on Boost upstream changes — from: would auto-uptake new Boost releases and expose your package to module-surface churn.

The subtree-1.81.0 tag in the repository's tag list is a one-off subtree-migration milestone, not a Boost release; ignore it for normal version selection.

Usage

[!NOTE] This package provides C++ headers, not Swift wrapper APIs. To use Boost types from Swift, you need a C++ bridging header with explicit type aliases and thin wrappers. This is a requirement of Swift/C++ interop — not all C++ patterns import directly into Swift.

C++ Bridging Header

Create a C++ header that instantiates the Boost templates you need:

#pragma once

#include <boost/algorithm/clamp.hpp>
#include <boost/optional.hpp>

// Expose a concrete template instantiation to Swift
using BoostOptionalInt = boost::optional<int>;

// Thin wrapper: Swift cannot call uninstantiated C++ function templates
inline int boost_clamp(int value, int lo, int hi) {
    return boost::algorithm::clamp(value, lo, hi);
}

// Thin wrapper: boost::optional accessors return references,
// which Swift considers interior pointers and blocks by default
inline int boost_optional_value(const boost::optional<int> &opt) {
    return opt.get();
}

Swift Consumer

import MyBridgingModule

let clamped = boost_clamp(15, 0, 10)  // 10

let opt = BoostOptionalInt(42)
let value = boost_optional_value(opt)  // 42

[!NOTE] For more detail on Swift/C++ interop patterns (type aliases for class templates, wrapping function templates, interior pointer limitations), see the Swift C++ Interop documentation. For a working external-consumer example, see Examples/LinuxConsumerProbe.

Development

Requirements

  • Swift 6.1+
  • C++17
  • macOS 13+ or Linux

Linux build verification

docker build .

The included Dockerfile builds and tests the package on swift:6.3, then builds Examples/LinuxConsumerProbe — an external-consumer smoke test that exercises the boost umbrella, the per-module products, all 37 modules in one translation unit, and a Swift target consuming Boost via C++ interop across a package boundary.

Contributing

Contributions are welcome. Read the 21-DOT-DEV contributing guidelines for general workflow, and AGENTS.md for project-specific architecture notes (modulemap stubs, subtree extraction flow, adding a new Boost module).

Security

For information on reporting security vulnerabilities, see the 21-DOT-DEV SECURITY.md.

License

This project is released under the MIT License. See LICENSE for details.

Boost libraries are distributed under the Boost Software License 1.0.

Package Metadata

Repository: 21-dot-dev/swift-boost

Default branch: main

README: README.md