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johnfairh/CRuby v2.0.0
Swift system module for libruby
⭐️ 9
🕓 1 year ago
.package(url: "https://github.com/johnfairh/CRuby.git", from: "v2.0.0")

Platforms License


Wrap libruby for SwiftPM or Xcode. Easily reconfigure for your Ruby installation.

See RubyGateway for a high-level Swift-Ruby integration framework.

Tested with environments:

  • macOS 11 system Ruby
  • macOS Homebrew, RBEnv, RVM
  • macOS bespoke installation
  • Ubuntu 20.04 x86_64 RBEnv, RVM, bespoke

And Ruby versions:

  • 2.6, 2.7, 3.0


CRuby comes set up to use the macOS system Ruby, and Xcode to provide C headers.

If you want to use a different Ruby then use the cfg-cruby script to rewrite the build config files.

For options other than macOS system Ruby, cfg-cruby generates a custom pkg-config file called CRuby.pc that can be passed directly to swift build or manually copied into your Xcode project settings.

Ruby 3's C interface header files use a non-default feature of Clang, the C compiler that the Swift tools use. Because of interesting Swift design choices, you must pass the -fdeclspec Clang flag when building a target that depends on CRuby.

Swift Package Manager

Include this repo as a dependency in your project:

.package(url: "https://github.com/johnfairh/CRuby/", majorVersion: 2)

To use a Ruby other than macOS system default you need to reconfigure. For example to set up Ruby 2.4.1 managed by rbenv:

swift package edit CRuby
./Packages/CRuby/cfg-cruby --mode rbenv --name 2.7.3
export PKG_CONFIG_PATH=$(pwd)/Packages/CRuby/CRuby.pc:$PKG_CONFIG_PATH
swift build

Either leave the CRuby package in edit mode or fork the repo, use that fork as your remote, and push your customizations back there.

If you are using Ruby 3 then you must pass an extra flag through to the C compiler:

swift build -Xcc -fdeclspec


Include this repo in your project. A git submodule works well. So either way you have a directory called CRuby. Then go to Build Settings for the Target where you want to do import CRuby and find Import Paths under Swift Compiler - Search Paths. Add the path to your CRuby directory - you can use ${SRCROOT} to substitute for the directory containing the project file.

Check Xcode is happy with an import CRuby line.

If you want to use a different Ruby, run cfg-cruby. Now transfer the settings from the CRuby.pc to the Xcode build settings for the target:

  1. Find Header Search Paths under Search Paths and add the directories mentioned in the Cflags: line of CRuby.pc. Don't copy over the -I part, just the paths.
  2. Find Library Search Paths under Search Paths and add the directories mentioned in the Libs: line of CRuby.pc. Don't copy over the -L part, just the paths. Ignore any -l flags [please tell me if you find a case where this breaks].
  3. If you are using Ruby 3, find Other Swift Flags under Swift Compiler - Custom Flags and add two flags: -Xcc -fdeclspec.

That's it: Xcode should now resolve CRuby against your chosen version.

Supported Ruby Configs

macOS system

Use the xcode-selected Xcode:

cfg-cruby --mode xcode

This configuration does not require a pkg-config file.

macOS Homebrew or Linux -dev package

cfg-cruby --mode pkgconfig --name <pkg-name>

Use pkg-config --list-all to see what you have installed.

The pkg-config setup is not directly consumable by SwiftPM. cfg-cruby uses it to create the CRuby.pc that is compatible with SwiftPM.

RBEnv or RVM

cfg-cruby --mode rbenv --name <version>


cfg-cruby --mode rvm --name <ruby name>

Something else

If you've built Ruby yourself or are using a different version manager that preserves the regular layout then:

cfg-cruby --path <full path to Ruby directory>

The path required is one to a directory that is called ruby-*something* and contains subdirectories including lib, include, and bin.


Welcome - github / johnfairh@gmail.com


Distributed under the MIT license.


Stars: 9
Last commit: 51 weeks ago
jonrohan Something's broken? Yell at me @ptrpavlik. Praise and feedback (and money) is also welcome.

Release Notes

1 year ago

Modernize, prep for Ruby 3.

  • Require Swift 5.4.
Bug Fixes
  • Fix --mode xcode option on macOS 11.

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