StoryboardやXibファイルからインスタンスを生成するprotocol ref: http://qiita.com/morizotter/items/f25bf03fa4e151703451

file0.txt

protocol InstantiateFromNibable {
    typealias Instance
    static func instantiateFromNib() -> Instance
}

file1.txt

final class LoadingFooterView: UIView, InstantiateFromNibable {
    static func instantiateFromNib() -> LoadingFooterView {
        return UINib(nibName: "LoadingFooterView", bundle: nil).instantiateWithOwner(nil, options: nil).first as! LoadingFooterView
    }

file2.txt

let footerView = LoadingFooterView.instantiateFromNib()

file3.txt

final class SearchViewController: UIViewController, InstantiateFromNibable {
    static func instantiateFromNib() -> SearchViewController {
        return UIStoryboard(name: "Search", bundle: nil).instantiateViewControllerWithIdentifier("SearchViewController") as! SearchViewController
    }

file4.txt

let vc = SearchViewController.instantiateFromNib()