ServiceLocator

Swift package offering a simple in-memory bucket into which services (i.e. objects) can be registered and retrieved.

Installation

1. Add this Swift package to your Xcode project's list of Swift packages by means of this repo's URL.
2. Select the target(s) that you would like to add this Swift package to.

Usage

The purpose of this Swift package is to offer a means by which an application can initialise and register all of its services into an in-memory bucket at start-up. Why? So that the application's view controllers and tests can obtain these services without having to concern themselves with the details of how these services are initialised.

The main class offered by this Swift package is the ServiceLocator class. This class defines three methods as follows:

• addService(service:) – Adds the given service to the service locator.
• addModule(module:) – Adds each of the services defined in the given Module to the service locator.
• getServiceOfType(type:) – Gets the service of the specified type from the service locator.

Registering services

Let's assume, for the purpose of example, that we're going to register services into a service locator grouped by modules rather than registering services individually. Let's assume also that our application consists of two modules – ModuleA and ModuleB – and ModuleA defines a service which ModuleB depends on. Then, firstly, ModuleA will look like this:

import ServiceLocator

class ModuleA: Module {
    func registerServices(in serviceLocator: ServiceLocator) throws {
        try serviceLocator.addService(ServiceA())
    }
}

Secondly, ModuleB will look like this:

import ServiceLocator

class ModuleB: Module {
    func registerServices(in serviceLocator: ServiceLocator) throws {
        let serviceA = try serviceLocator.getServiceOfType(ServiceA.self)
        let serviceB = ServiceB(serviceA)

        try serviceLocator.addService(serviceB)
    }
}

Lastly, the ServiceLocator object will be defined as follows:

let serviceLocator = ServiceLocator()

try serviceLocator.addModule(ModuleA())
try serviceLocator.addModule(ModuleB())

Retrieving services

The only two places where services should be sought out from a ServiceLocator object (once it has been defined and all services have been added to it) are the application's view controllers and test classes. All other calls to the ServiceLocator.getServiceOfType(type:) method are considered an abuse.

Assume that a view controller or test class has access to a ServiceLocator object named serviceLocator. A service is retrieved from this ServiceLocator object as follows:

@Inject(via: serviceLocator) var someService: SomeService