An enhancement built on top of Foundation Framework and XCTest. Performance test assertions and the magic ?! operator among many. We primarily use it for server-side engineering.


Beton is a Swift library built on top of the Foundation framework, that provides an additional layer of functionality, including easy localization, performance test measurement support, and convenience functionality. For us, Beton is primarily, but not exclusively, useful for server-side Swift engineering.


  • Beton: Generic purpose functionalities that may be useful for every application.
  • XCTBeton: Extends the capabilities of XCTest by providing assertions for performance measurements.

Using the Beton Module


To use Beton simply import it. If you need anything from Foundation you do not need to explicitly import it. You get it for free by importing Beton.

import Beton

Convenience API for Bundle

Using Beton it is quite easy to get localized bundles and values from them.

Suppose you have a localization bundle in your project for the hu_HU locale, with a translation for "Apple" = "Alma" , but you don't have one for "Banana" (which would be "Banán"). The following example finds the bundle, gets the localized version of "Apple", and falls back to the given key "Banana".

let bundle          = Bundle.module.localizationBundles["hu_HU"]
let localizedApple  = bundle?.localizedString("Apple")
// localizedApple == "Alma"
let localizedBanana = bundle?.localizedString("Banana")
// localizedBanana == "Banana"

Convenience API for Locale

Locales in Beton are expressible by string literals.

let locales: [Locale] = ["en_US", "en_GB", "hu_HU"]
for locale in locales {
  print("Currency symbol: \(locale.currencySymbol ?? "N/A")")
// Prints:
// Currency symbol: $
// Currency symbol: £
// Currency symbol: Ft

?! operator

The ?! operator unwraps an Optional value if is not nil, otherwise throws the given error.

struct GenericError: Error {}

let answer = try Int("42") ?! GenericError()
// answer == 42

try Int("NaN") ?! GenericError()
// Throws: GenericError()

sum extension on Sequences

Calculates the total of all elements in a sequence. Available on any sequence with values that conform to AdditiveArithmetic

let arraySum = [1.1, 2.2, 3.3, 4.4, 5.5].sum()
// arraySum == 16.5

let rangeSum = (1..<10).sum()
// rangeSum == 45

let setSum = Set(arrayLiteral: 1, 2, 3, 2, 3).sum()
// setSum == 6

Convenience for Measurements

In Beton measurements have default units and they conform to AdditiveArithmetic.

let sum = [1, 2, 3].map { Measurement<UnitLength>(value: $0, unit: .default) }.sum()
// sum == 6.0 m

Using the XCTBeton Module

Let's say you have a simple performance test that measures some code. Using XCTest there is no easy, straightforward way to make assertions to the performance results.

import XCTest

class PerformanceTests: XCTestCase {
  func test_measureSum() {
    measure {
      let _ = (1..<1000).reduce(0, +)
    // Performance assertions needed!

You can turn this code into an XCTBeton test by simply changing the import. Yes, that's it. You can now make assertions!

import XCTBeton

class PerformanceTests: XCTestCase {
  func test_measureSum() {
    measure {
      let _ = (1..<1000).reduce(0, +)
    XCTAssertMetric(.clock, .timeMonotonic, .average(maximum: 0.001))

If you want to control the type of measurements, and how many times the tests run you can do that using the same API as you would in regular XCTest.

import XCTBeton

class PerformanceTests: XCTestCase {
  func test_measureSum() {
    let options = XCTMeasureOptions()
    options.iterationCount = 100
    measure(metrics: [XCTCPUMetric(), XCTMemoryMetric()], options: options) {
      let _ = (1..<1000).reduce(0, +)
    XCTAssertMetric(.cpu, .time, .average(maximum: 0.002))
    XCTAssertMetric(.cpu, .cycles, .average(maximum: 2000))
    XCTAssertMetric(.memory, .physical, .average(maximum: 20))

Adding Beton as a Dependency

To use the Beton library in a SwiftPM project, add it to the dependencies for your package and your target. Your target can depend on either the Beton or XCTBeton modules, or both.

// swift-tools-version:5.5.0

import PackageDescription

let package = Package(
  name: "MyApplication",
  dependencies: [
    .package(url: "", from: "1.0.0"),
  targets: [
    .target(name: "MyApplication", dependencies: [
      .product(name: "Beton", package: "Beton"),
      .product(name: "XCTBeton", package: "Beton"),


  • Swift Tools 5.5.0
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Last updated: Tue Jun 28 2022 20:16:57 GMT-0500 (GMT-05:00)