Swiftpack.co - Package - nsagora/validation-toolkit

Validation Toolkit

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  1. Introduction
  2. Requirements
  3. Installation
  4. Usage Examples
  5. Contribute
  6. Meta


ValidationToolkit is designed to be a lightweight framework specialised in user data validation, such as email format, input length or passwords matching.

At the core of this project are the following principles:

  • Separation of concerns
  • Availability on all platforms
  • Open to extensibility

Separation of concerns

Think of ValidationToolkit as to an adjustable wrench more than to a Swiss knife. With this idea in mind, the toolkit is composed from a small set of protocols, classes and structs than can be easily used to fit your project needs.

All platforms availability

Since validation can take place at many levels, ValidationToolkit was designed to support iOS, macOS, tvOS, watchOS and native Swift projects, such as server apps.

Open to extensibility

Every project is uniq in it's challenges and it's great when we can focus on solving them instead on focusing on boilerplate tasks. While ValidationToolkit is compact and offers all you need to build validation around your project needs, it also includes a set of common validations that most of the projects can benefit of. This includes validation predicates for email, required fields, password matching, url and many more to come.


  • iOS 8.0+ / macOS 10.10+ / tvOS 9.0+ / watchOS 2.0+
  • Xcode 8.1+
  • Swift 3.0+



You can use Carthage to install ValidationToolkit by adding it to your Cartfile:

github "nsagora/validation-toolkit"

Run carthage update to build the framework and drag the built ValidationToolkit.framework into your Xcode project.

Setting up Carthage

Carthage is a decentralised dependency manager that builds your dependencies and provides you with binary frameworks.

You can install Carthage with Homebrew using the following command:

$ brew update
$ brew install carthage


You can use CocoaPods to install ValidationToolkit by adding it to your Podfile:

source 'https://github.com/CocoaPods/Specs.git'
platform :ios, '8.0'

target 'YOUR_TARGET_NAME' do
	pod 'ValidationToolkit'

Then, run the following command:

$ pod install

Note that this requires CocoaPods version 1.0.0, and your iOS deployment target to be at least 8.0.

Setting up CocoaPods

CocoaPods is a dependency manager for Cocoa projects. You can install it with the following command:

$ gem install cocoapods

Swift Package Manager

You can use the Swift Package Manager to install ValidationToolkit by adding it to your Package.swift file:

import PackageDescription

let package = Package(
    name: "YOUR_PROJECT_NAME",
    targets: [],
    dependencies: [
        .Package(url: "https://github.com/nsagora/validation-toolkit", majorVersion: 1),

Note that the Swift Package Manager is still in early design and development, for more information checkout its GitHub Page.


To use this library in your project manually you may:

  1. for Projects, just drag the Sources folder into the project tree
  2. for Workspaces, include the whole ValidationToolkit.xcodeproj

Usage example

For a comprehensive list of examples try the ValidationToolikit.playground:

  1. Download the repository locally on your machine
  2. Open ValidationToolkit.workspace
  3. Build ValidationToolkit iOS target
  4. Select the ValidationToolkit playgrounds from the Project navigator.


The Predicate represents the core protocol and has the role to evaluate if an input matches on a given validation condition.

At ValidationToolkit's core we have the following two predicates, which allow developers to compose predicates specific to the project needs.

let predicate = RegexPredicate(expression: "^[a-z]$")
predicate.evaluate(with: "a") // returns true
predicate.evaluate(with: "5") // returns false
predicate.evaluate(with: "ab") // returns false
let pred = BlockPredicate<String> { $0.characters.count > 2 }
predicate.evaluate(with: "a") // returns false
predicate.evaluate(with: "abc") // returns true

In addition, the toolkit offers a set of common validation predicates that your project can benefit of:

let predicate = EmailPredicate()
predicate.evaluate(with: "hello@") // returns false
predicate.evaluate(with: "hello@nsagora.com") // returns true
predicate.evaluate(with: "héllo@nsagora.com") // returns true
let predicate = URLPredicate()
predicate.evaluate(with: "http://www.url.com") // returns true
predicate.evaluate(with: "http:\\www.url.com") // returns false
let predicate = PairMatchingPredicate()
predicate.evaluate(with: ("swift", "swift")) // returns true
predicate.evaluate(with: ("swift", "obj-c")) // returns false

On top of that, developers can build more advanced or complex predicates by extending the Predicate protocol, and/ or by composing or decorating the existing predicates:

Custom Predicate
public class MinLenghtPredicate: Predicate {

    public typealias InputType = String

    private let minLenght:Int

    public init(minLenght:Int) {
        self.minLenght = minLenght

    public func evaluate(with input: String) -> Bool {
        return input.characters.count >= minLenght

let predicate = MinLenghtPredicate(minLenght: 5)
predicate.evaluate(with: "alph") // returns false
predicate.evaluate(with: "alpha") // returns true
predicate.evaluate(with: "alphabet") // returns true


A Constraint represents a structure that links a Predicate to an Error, in order to provide useful feedback for the end users.

`Constraint` Example
let predicate = BlockPredicate<String> { $0 == "Mr. Goodbytes" }
let constraint = Constraint(predicate: predicate, error: MyError.magicWord)

let result = constraint.evaluate(with: "please")
switch result {
case .valid:
    print("access granted...")
case .invalid(let error as MyError):
enum MyError:Error {
    case magicWord

extension MyError: LocalizedError {
    var errorDescription:String? {
        return "Ah Ah Ah! You didn't say the magic word!"

Constraint Sets

A ConstraintSet represents a collection of constraints that allows the evaluation to be made on:

  • any of the constraints
  • all constraints

To provide context, a ConstraintSet allows us to constraint an input as being required and also as being a valid email.

`ConstraintSet` Example

The classic validation example is that of the login form, whereby users are prompted to enter their username and password. This process typically entails some form of validation, but the logic itself is often unstructured and spread out through a view controller. Similarly, the logic is often invoked through various user interactions (e.g. typing characters into a field, and tapping a Login button).

ValidationToolkit seeks instead to consolidate, standardise, and make explicit the logic that is being used to validate user input. To this end, the below example demonstrates construction of a full ConstraintSet object that can be used to enforce requirements on the username input data:

// Setup a `Constraint` used to check the length of the username
let usernameLengthConstraint = { () -> Constraint<String> in
    let pred = BlockPredicate<String> { $0.characters.count > 2 }
    return Constraint(predicate: pred, error: FormError.UserName.tooShort)

// Setup a `Constraint` used to check the characters contained within the username
let usernameCharactersConstraint = { () -> Constraint<String> in
    let pred = RegexPredicate(expression: "^[0-9a-Z_\\-]*?$")
    return Constraint<String>(predicate: pred, error: FormError.UserName.invalidCharacters)

// Create our `ConstraintSet` to compose the two constraints
let usernameConstraints = [usernameLengthConstraint, usernameCharactersConstraint];
let usernameValidator = ConstraintSet<String>(constraints: usernameConstraints)

// Evaluate user input, and collect results
let results = usernameValidator.evaluateAll(input: "nsagora")
let errorMessages = results.flatMap { result -> String? in
    switch result {
    case .valid:
        return nil
    case .invalid(let error):
        return error.localizedDescription

// Define form errors

enum FormError {

    enum UserName:Error {
        case tooShort
        case invalidCharacters

extension FormError.UserName: LocalizedError {

    var errorDescription:String? {
        switch self {
        case .tooShort:
            return "Username must be at least 3 characters long."
        case .invalidCharacters:
            return "Username must only contain alphanumeric characters, dashes, and underscores."

From above, we see that once we've constructed the usernameValidator, we're simply calling evaluateAll(input:) to get a list of results. These results we can then map into an array of error messages, which we can handle as we please. You can imagine that we might construct this usernameValidator once, and simply evaluate it against the user input data when we want to perform validation on the username.


We would love you for the contribution to ValidationToolkit, check the LICENSE file for more info.


This project is developed and maintained by the members of iOS NSAgora, the community of iOS Developers of Iași, Romania.

Distributed under the MIT license. See LICENSE for more information.


Credits and references

We got inspired from other open source projects and they worth to be mentioned below for reference:

  • https://github.com/adamwaite/Validator
  • https://github.com/jpotts18/SwiftValidator


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0.5.0 - Jul 21, 2017

  • Change license from Apache License to MIT License
  • Simplify names

0.2.0 - Mar 4, 2017

0.3.0 - Mar 4, 2017

0.4.1 - Mar 4, 2017

0.4.0 - Feb 26, 2017