An alternative way to specify RequestTemplate

RequestTemplate.swift

// So this is the same...

public enum HTTPMethod: String {
    case get = "GET"
    case post = "POST"
    case put = "PUT"
    case delete = "DELETE"
    case patch = "PATCH"
}

public protocol RequestTemplate {
    var method: HTTPMethod { get }
    var path: String { get }
    var parameters: [URLQueryItem] { get }
    var headers: [String: String] { get }
    var body: Data? { get }
}

// But now we specify this...

public extension RequestTemplate {
    var method: HTTPMethod { return .get }
    var parameters: [URLQueryItem] { return [] }
    var body: Data? { return nil }
    var headers: [String : String] { return [:] }
}

// Which allows us to define requests with less boilerplate 👇

struct GetCardsRequest: RequestTemplate {
    let path: String = "cards/"
}

// And if you want to run it, use this 👇

public class ScryfallServer {
    let baseURL: URL(string: "https://api.scryfall.com")!

    public func taskForRequest(_ request: RequestTemplate,
                               completion: @escaping (Result<Data, Error>) -> Void) -> URLSessionTask? {
        guard let urlRequest = URLRequest(with: request, baseURL: baseURL) else {
            return nil
        }

        let dataTask = URLSession.shared.dataTask(with: urlRequest) { (data, response, error) in
            if let error = error {
                completion(.failure(error))
            } else if let data = data {
                completion(.success(data))
            }
        }

        return dataTask
    }
}