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Embed Ruby in Swift: load Gems, run Ruby scripts, get results.

RubyGateway is a framework built on the Ruby C API that lets Swift programs running on macOS or Linux painlessly and safely run and interact with Ruby programs. It's easy to pass Swift datatypes into Ruby and turn Ruby objects back into Swift types.

This project is young: various things missing including collection types which should come with Swift 4.1. Eventually plan to allow implementation of Ruby classes in Swift enabling Ruby as a sandboxed DSL/scripting language for Swift applications.

See CRuby if you are looking for a low-level Ruby C API wrapper.


A couple of examples:


Rouge is a code highlighter. In Ruby:

require 'rouge'
html = Rouge.highlight("let a = 3", "swift", "html")

In Swift 4 with similar [lack of] error checking:

import RubyGateway

try! Ruby.require("rouge")
let html = try! Ruby.get("Rouge").call("highlight", args: ["let a = 3", "swift", "html"])

In future Swift:

import RubyGateway

try! Ruby.require("rouge")
let html = Ruby.Rouge!.highlight("let a = 3", "swift", "html")!


// Create an object.  Use keyword arguments with initializer
let student = RbObject(ofClass: "Academy::Student", kwArgs: [("name", "barney")])!

// Acess an attribute
print("Name is \(student.get("name"))"

// Fix their name by poking an ivar
try! student.setInstanceVar("@name", newValue: "Barney")

// Get a Swift version of `:reading`
let readingSubject = RbSymbol("reading")

// Call a method with mixed Swift data types
try! student.call("add_score", args: [readingSubject, 30])
try! student.call("add_score", args: [readingSubject, 35])

// Get a result as floating point
let avgScoreObj = try! student.call("mean_score_for_subject", args: [readingSubject])
let avgScore = Double(avgScoreObj)!
print("Mean score is \(avgScore)")

// Pass Swift code as a block
let scores = try! student.get("all_scores")
scores.call("each") { args in
    print("Subject: \(args[0]) Score: \(args[1])")
    return .nilObject



  • Swift 4 or later, from swift.org or Xcode 9.2+.
  • macOS (tested on 10.13.3) or Linux (tested on Ubuntu Xenial/16.04 on x86_64) with Clang 6+.
  • Ruby 2.2 or later including development files:
    • For macOS, this comes with Xcode.
    • For Linux you may need to install a -dev package depending on how your Ruby is installed.
    • RubyGateway requires 'original' MRI/CRuby Ruby - no JRuby/Rubinius/etc.


For macOS, if you are happy to use the system Ruby then you just need to include the RubyGateway framework as a dependency. If you are building on Linux or want to use a different Ruby then you also need to configure CRuby.

Getting the framework

Carthage for macOS:

github "johnfairh/RubyGateway"

Swift package manager for macOS or Linux:

.package(url: "https://github.com/johnfairh/RubyGateway", from: "0.1.0")

CocoaPods for macOS:

pod 'RubyGateway'

Configuring CRuby

CRuby is the glue between RubyGateway and your Ruby installation. It is a separate github project but RubyGateway includes it as submodule so you do not install or require it separately.

By default it points to the macOS system Ruby. Follow the CRuby usage instructions to change this. For example on Linux using Brightbox Ruby 2.5:

sudo apt-get install ruby2.5 ruby2.5-dev pkg-config
mkdir MyProject
swift package init --type executable
vi Package.swift
# add RubyGateway as a package dependency (NOT CRuby)
# add RubyGateway as a target dependency
echo "import RubyGateway; print(Ruby.versionDescription)" > Sources/MyProject/main.swift
swift package update
swift package edit CRuby
Packages/CRuby/cfg-cruby --mode pkg-config --name ruby-2.5
PKG_CONFIG_PATH=$(pwd)/Packages/CRuby:$PKG_CONFIG_PATH swift run


Welcome: open an issue / johnfairh@gmail.com


Distributed under the MIT license.


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