Route collections allow multiple routes and route groups to be organized in different files or modules.

Here is an example of a route collection for the v1 portion of an API.

import Vapor
import HTTP
import Routing

class V1Collection: RouteCollection {
    typealias Wrapped = HTTP.Responder
    func build<B: RouteBuilder>(_ builder: B) where B.Value == Wrapped {
        let v1 = builder.grouped("v1")
        let users = v1.grouped("users")
        let articles = v1.grouped("articles")

        users.get { request in
            return "Requested all users."
        }

        articles.get(Article.self) { request, article in
            return "Requested \(article.name)"
        }
    }
}

This class could be place in any file, and we could add it to our droplet or even another route group.

let v1 = V1Collection()
drop.collection(v1)

The Droplet will then be passed to the build(_:) method of your route collection and have the various routes added to it.

For those that are curious, let's break down the route collection line by line to better understand what is going on.

typealias Wrapped = HTTP.Responder

This limits our route collection to adding HTTP responders. While the underlying router is capable of routing any type, Vapor routes HTTP responders exclusively. If we want to use this route collection with Vapor, it's wrapped type needs to match.

func build<B: RouteBuilder>(_ builder: B) where B.Value == Wrapped {

This method accepts a route builder and also verifies that the route builder accepts Wrapped or, as defined in the last line, HTTP.Responders. Vapor's Droplet and any route group created with Vapor are RouteBuilders that accept HTTP responders.

let v1 = builder.grouped("v1")

From there you can create routes with the builder as usual. The builder: B will work exactly like a Droplet or route group. Any methods that work there will work on this builder.

You can even add EmptyInitializable to your route collection if it has an empty init method. This will allow you to add the route collection via its type name.

class V1Collection: RouteCollection, EmptyInitializable {
    init() { }
    ...

Now we can add the collection without initializing it.

drop.collection(V1Collection.self)