Swift singleton with initialization injection

singleton.swift

class CoreGlobal {
    fileprivate static let shared = CoreGlobal()
    fileprivate let device: DeviceManager

    private class Config {
        var deviceManager: DeviceManager?
    }
    private static let config = Config()
    
    @discardableResult
    public static func setup(with deviceManager: DeviceManager) -> CoreGlobal {
        CoreGlobal.config.deviceManager = deviceManager
        return CoreGlobal.shared
    }
    private init() {
        guard let deviceManager = CoreGlobal.config.deviceManager else {
            fatalError("Must call `setup(_:)` first.")
        }
        
        device = deviceManager
    }
}