Configuration is a key-value storage. It is mainly used to set default values in classes like BaseController or ViewBase.

Configuration provides these methods for storing and retrieving values:

class Configuration {

    func set<T>(_ property: Property<T>, to value: T)

    func get<T>(valueFor property: Property<T>) -> T


As you can see, Configuration uses Property as keys.

struct Property<T> {

    let id: Int
    let defaultValue: T

    init(defaultValue: T)

Property defines type of value it points to (T). Field id is unique identifier for each object. So in order to retrieve value previously stored, you have to use the same instance of Property (passing Property by value doesn’t change id).


let configuration = Configuration()

let integer = Property(defaultValue: 1)
let optionalInteger = Property<Int?>()

configuration.get(valueFor: integer) 			// returns 1
configuration.get(valueFor: optionalInteger) 	// returns nil

configuration.set(integer, to: 5)
configuration.set(optionalInteger, to: 0)

configuration.get(valueFor: integer) 			// returns 5
configuration.get(valueFor: optionalInteger) 	// returns 0

Notice that defaultValue from Property.init is used when no value for that Property was previously stored inside Configuration. Also Optional types do not require defaultValue, in that case it will be nil.

To create custom property simply make a new instance of Property:

let newProperty = Property<Int>(defaultValue: 0)

It is recommended to put it inside an extension of Properties (see below).


Properties is a struct used to store instances of Property. Each part of Reactant can define new properties by simply adding them to Properties by extension. For example:

extension Properties {

	static let layoutMargins = Property<UIEdgeInsets>(defaultValue: .zero)

Concrete instances of Property are covered in documentation for parts of Reactant which uses them.

Global and custom configuration

Global configuration is a special instance of Configuration accessible by This configuration is the default one for all things in Reactant. It is applied at the end of init.

If you need to change configuration but only for certain classes. You can create your own instance of Configuration by calling init(copy: Configuration...). Notice the optional copy parameter through which you can “inherit” the common settings for example from After that you can make your changes, while leaving the intact. It’s variadic as well, allowing you to copy configuration from multiple Configuration instances. Most likely that will result in conflict of some properties. In that case the priority is: init(copy: leastSignificant, ..., mostSignificant). When you have your custom Configuration ready, assign it to instance of Configurable by instance.configuration = customConfiguration.


Configurable is a helping protocol for classes that want to use data from Configuration.

protocol Configurable: class {

    var configuration: Configuration { get set }

extension Configurable {

    /// Calls didSet on configuration.
    func reloadConfiguration()

    /// Applies configuration to this object and returns it to allow chaining.
    func with(configuration: Configuration) -> Self

You should access configuration only from its didSet listener. This ensures that everything is properly changed together with the Configuration instance.

This exempt from ControllerBase shows how to implement Configurable from scratch:

class ControllerBase ... {


	var configuration: Configuration = .global { // Default configuration is .global.
	    didSet {
	        (rootView as? Configurable)?.configuration = configuration // New instance of configuration is propagated through the dependency tree.
	        navigationItem.backBarButtonItem = configuration.get(valueFor: Properties.defaultBackButton) // Accessing values.

	init() {
		reloadConfiguration() // didSet is not called when default value is assigned. This must be called after the class is initialized.



You will usually inherit from some class that already implements Configurable making it much easier for you to use configuration:

class CustomView: ViewBase... { // ViewBase implements Configurable

	override var configuration: Configuration { // No .global assignment (already in super class).
		didSet {
		    ... // Do something.

	// No call of reloadConfiguration() (done in super.init).