point free caching github api example

github.swift

let cachingGitHub = CachingGitHub()
struct GitHub {
    var latestRepos: () -> [Repo] =  { return cachingGitHub.latestRepos }
    var fetchRepos: (@escaping (Result<[Repo], APIError>) -> Void) -> Void = cachingGitHub.fetchRepos
}

class CachingGitHub {
    var latestRepos = [Repo]()
    
    func fetchRepos(completion: @escaping (Result<[Repo], APIError>) -> Void) {
        _fetchRepos { result in
            switch result {
            case .success(let repos):
               self.latestRepos = repos
            default:
                break
            }
            completion(result)
        }
    }
}

static func _fetchRepos : (@escaping (Result<[Repo], APIError>) -> Void) -> Void {
    ...
}

private var latestRepos: [Repo] {
  get { return latestReposQueue.sync { _latestRepos } }
  set { latestReposQueue.async { _latestRepos = newValue } }
}
private let latestReposQueue = DispatchQueue(label: "latestRepos")
private var _latestRepos: [Repo] = []