FuncExample.swift

public protocol HandlesStack {

    func setStack(_: [Segment])
}

public protocol Router {

    typealias Delegate

    var handlesPath: Path -> Bool { get }

    var setPath: Path -> Bool { get }

    var delegate: Delegate { get }
}

public struct StackRouter<Delegate where Delegate: HandlesStack>: Router {

    public let handlesPath: Path -> Bool

    public let setPath: Path -> Bool

    public let delegate: Delegate

    public init(handlesPath: Path -> Bool, setPath: Path -> Bool, delegate: Delegate) {
        self.handlesPath = handlesPath
        self.setPath = setPath
        self.delegate = delegate
    }

}

public func createStackRouter<Delegate where Delegate: HandlesStack>(pattern: String, children: [Route] = [], delegate: Delegate) -> StackRouter<Delegate> {

    let handlesPath: Path -> Bool = { path in
        guard let (_, remainder) = path.splitBy(pattern) else { return false }
        return children.contains { $0.handlesPath(remainder) }
    }

    let setPath: Path -> Bool = { path in
        guard let pathRemainder = path.replace(pattern, "") else { return false }
        guard let stack = buildStack(pathRemainder, children) else { return false }
        delegate.setStack(stack)
        return true
    }

    return StackRouter(handlesPath: handlesPath, setPath: setPath, delegate: delegate)
}

StructExample.swift

public protocol HandlesStack {

    func setStack(_: [Segment])
}

public protocol Router {

    typealias Delegate

    var handlesPath: Path -> Bool { get }

    var setPath: Path -> Bool { get }

    var delegate: Delegate { get }
}

public struct StackRouter<Delegate where Delegate: HandlesStack>: Router {

    public let handlesPath: Path -> Bool

    public let setPath: Path -> Bool

    public let delegate: Delegate

    public init(pattern: String, children: [Route] = [], delegate: Delegate) {

        handlesPath = { path in
            guard let (_, remainder) = path.splitBy(pattern) else { return false }
            return children.contains { $0.handlesPath(remainder) }
        }

        setPath = { path in
            guard let pathRemainder = path.replace(pattern, "") else { return false }
            guard let stack = buildStack(pathRemainder, children) else { return false }
            delegate.setStack(stack)
            return true
        }

        self.delegate = delegate
    }
}

Usage.swift

let routerFromStruct = StackRouter(pattern: pattern, children: children, delegate: delegate)

// -- vs --

let routerFromFunc = createStackRouter(pattern: pattern, children: children, delegate: delegate)


// **Further note**: the init function from the struct can be converted to same type as createStackRouter using:
let structCreateStackRouter: (String, [Route], Delegate) -> StackRouter<Delegate> = StackRouter<Delegate>.self.init