1. 조합 모드

/**     （   《Head First    》）：
                  “  /  ”    。
                          
**/

protocol FileType {
    func getFileName() -> String
    func addFile(file: FileType)
    func deleteFile(file: FileType)
    func display()
}
//                 ，            
extension FileType {
    func addFile(file: FileType) {}
    func deleteFile(file: FileType){}
}

class Folder: FileType {
    private var files: Dictionary = Dictionary()
    private var folderName: String
    init(folderName: String) {
        self.folderName = folderName
    }
    
    func getFileName() -> String {
        return self.folderName
    }
    
    func addFile(file: FileType) {
        files[file.getFileName()] = file
    }
    
    func deleteFile(file: FileType) {
        files.removeValue(forKey: file.getFileName())
    }
    
    func display() {
        let allKeys = Array(files.keys)
        print(getFileName())
        for i in 0.. String {
        return self.fileName
    }
    
    func display() {
        print(getFileName())
    }
}

class SwiftFile: BaseFile {
}

class ObjCFile: BaseFile {
}

//Test
//      
let rootFolder: FileType = Folder(folderName: "    ")
let objcFile1: FileType = ObjCFile(fileName: "objc1.h")
let swiftFile1: FileType = SwiftFile(fileName: "file1.Swift")
rootFolder.addFile(swiftFile1)
rootFolder.addFile(objcFile1)

let subFolder : FileType = Folder(folderName: "    ")
let objcFile2: FileType = ObjCFile(fileName: "objc2.h")
let swiftFile2: FileType = SwiftFile(fileName: "file2.Swift")
subFolder.addFile(swiftFile2)
subFolder.addFile(objcFile2)

rootFolder.addFile(subFolder)

//                
rootFolder.display()