Hands-On Design Patterns with Swift

Generic types

You can also make complex types generic. In our example, we created this wrapper around a list of Runnable, called ManyRunner. The job of a many runner is to run all of the runnables. The ManyRunner is itself Runnable, so we have created a kind of type recursion, as follows:

struct ManyRunner<T>: Runnable where T: Runnable {    let runnables: [T]    func run() {        runnables.forEach { $0.run() }    }}

Let's also provide a base object that runs a simple Incrementer. Each time the Incrementer is run, the static count will increment, to keep track of the number of invocations:

struct Incrementer: Runnable {    private(set) static var count = 0    func run() {        Incrementer.count += 1    }}

When using generics on types, remember that the types have to ...