Injecting dependencies by value, scenario 2

conf_deps_by_value2.swift

import Foundation

// MARK: - (1) Original app blob scenario:

/// We have the app blob with original code:
/// _Note: We use enums just for namespaces._
enum AppBlob {
    /// Some sigleton (global state):
    static var someSingleton: String?
    /// Some view:
    struct UIView {
        init() {
            /// We depend on the singleton to create an instance:
            precondition(AppBlob.someSingleton != nil)
        }
        func load() {}
    }
    /// The builder:
    struct Builder {
        func build() {
            /// In the original code, the singleton initialization comes first:
            AppBlob.someSingleton = "bla-bla-bla"
            /// Next, we handle the view:
            let view = UIView()
            view.load()
        }
    }
}

/// Run:
do {
    /// Create a builder and run it:
    let builder = AppBlob.Builder()
    builder.build()
}

// MARK: - (2) After modularization scenario:

/// Here we have modularized the constructor into some module. The only change is that we now use the configuration object to inject dependencies:
enum SomeModule {
    /// The configuration object to host injected dependencies:
    struct Configuration {
        let view: AppBlob.UIView
    }
    /// The builder moved to `SomeModule`:
    struct Builder {
        let cfg: Configuration
        func build() {
            /// In the original code, the singleton initialization comes first:
            AppBlob.someSingleton = "bla-bla-bla"
            /// Next, we handle the view (this time the readymade view-dependency is provided by the configuration object):
            cfg.view.load()
        }
    }
}

/// Run:
do {
    /// Make sure the singleton is originally non-initialized:
    AppBlob.someSingleton = nil
    /// Create a configuration object to pass dependincies to the builder:
    let cfg = SomeModule.Configuration(view: AppBlob.UIView())
    /// Create the builder and run it:
    let builder = SomeModule.Builder(cfg: cfg)
    builder.build()
}