WIP

TypeEraseSample.swift

import UIKit
import Foundation
import XCPlayground
import PlaygroundSupport

//protocol Pokemon {
//    associatedtype PokemonType
//    func attack(move: PokemonType) -> Void
//}
//
//class Electric {}
//class Fire {}
//
//class Pikachu: Pokemon {
//    typealias PokemonType = Electric
//    func attack(move: Electric) {
//        print("⚡️")
//    }
//}
//
//class Charmander: Pokemon {
//    typealias PokemonType = Fire
//    func attack(move: Fire) {
//        print("🔥")
//    }
//}
//
//let pika1: Pikachu = Pikachu()
//// Pokemonプロトコルに準拠してるのにPokemonTypeが決まってないのでコンパイルエラー
//// let pika2: Pokemon = Pikachu()
//
//class AnyPokemon<PokemonType>: Pokemon {
//    private let _attack:((PokemonType) -> Void)
//
//    required init<U:Pokemon>(_ pokemon: U) where U.PokemonType == PokemonType {
//        self._attack = pokemon.attack
//    }
//
//    func attack(move: PokemonType) {
//        return _attack(move)
//    }
//}

//: Playground - noun: a place where people can play

// classを継承しないと ‘weak’ cannot be applied to non-class type というコンパイルエラー
// プロトコル、構造体、列挙体はweakにできないが、クラスおよびクラスを継承したものだけはweakに出来る。
protocol ViewControllerDelegate: class {
    associatedtype Item
    
    func collectionView(_ collectionView: UICollectionView, cellFor item: Item) -> UICollectionViewCell?
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeFor item: Item) -> CGSize?
    func collectionView(_ collectionView: UICollectionView, didSelect item: Item)
    
    func collectionView(_ collectionView: UICollectionView,
                        cellFor item: Item,
                        dequeue: ((_ identifier:String) -> UICollectionViewCell?)
        ) -> UICollectionViewCell?
}

// 型消去用クラス
class ViewControllerDelegateWrapper<Delegate: ViewControllerDelegate> {
    private weak var delegate: Delegate?
    
    init(delegate: Delegate) {
        self.delegate = delegate
    }
    
    func collectionView(_ collectionView: UICollectionView, cellFor item: Delegate.Item) -> UICollectionViewCell? {
        return delegate?.collectionView(collectionView, cellFor: item)
    }
    
    func collectionView(_ collectionView: UICollectionView,
                        cellFor item: Delegate.Item,
                        dequeue: ((_ identifier:String) -> UICollectionViewCell?)
        ) -> UICollectionViewCell? {
        return delegate?.collectionView(collectionView, cellFor: item, dequeue: dequeue)
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeFor item: Delegate.Item) -> CGSize? {
        return delegate?.collectionView(collectionView, layout: collectionViewLayout, sizeFor: item)
    }
    
    func collectionView(_ collectionView: UICollectionView, didSelect item: Delegate.Item) {
        self.delegate?.collectionView(collectionView, didSelect: item)
    }
}

class ViewController<Delegate: ViewControllerDelegate>: UICollectionViewController, UICollectionViewDelegateFlowLayout {
    //associatedtypeのItemが決定していないのでコンパイルエラー
    //weak var delegate: MyViewControllerDelegate?
    
    typealias CellRegisterHandler = ((_ cellClass: AnyClass, _ identifier: String) -> Void)
    
    //型消去用のクラスをdelegateにしてGenericsに扱う
    var delegate: ViewControllerDelegateWrapper<Delegate>?
    
    var items = [Array<Delegate.Item>]()
    
    //MARK: - initializer
    
    init(_ delegate: ViewControllerDelegateWrapper<Delegate>, configure: CellRegisterHandler) {
        super.init(collectionViewLayout: UICollectionViewFlowLayout())
        self.delegate = delegate
        let register: CellRegisterHandler = { [weak self] (cellClass: AnyClass, identifier: String) in
            self?.collectionView.register(cellClass, forCellWithReuseIdentifier: identifier)
        }
        
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    //MARK: - view lifecycle
    
    override func viewDidLoad() {
         super.viewDidLoad()
    }
    
    //MARK: - UICollectionViewDataSource
    
    override func numberOfSections(in collectionView: UICollectionView) -> Int {
        return items.count
    }
    
    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return items[section].count
    }
    
    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        
        let item = items[indexPath.section][indexPath.row]
        
        let dequeueHandler = dequeue(collectionView: collectionView, from: indexPath)
        if let cell = delegate?.collectionView(collectionView, cellFor: item, dequeue: dequeueHandler) {
            return cell
        }
        
        return collectionView.dequeueReusableCell(withReuseIdentifier: "Identifier", for: indexPath)
    }
    
    //MARK: - UICollectionViewDelegate

    override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let item = items[indexPath.section][indexPath.row]
        delegate?.collectionView(collectionView, didSelect: item)
    }
    
    //MARK: - UICollectionViewLayout
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let item = items[indexPath.section][indexPath.row]
        if let size = delegate?.collectionView(collectionView, layout: collectionViewLayout, sizeFor: item) {
            return size
        }
        return collectionViewLayout.collectionViewContentSize
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return 1
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
        return 0
    }
    
    //MARK: - MISC
    
    private func dequeue(collectionView: UICollectionView, from indexPath: IndexPath)
        -> ((_ identifier:String) -> UICollectionViewCell?) {
            return { (_ identifier:String) -> UICollectionViewCell? in
                return collectionView.dequeueReusableCell(withReuseIdentifier: identifier, for: indexPath)
            }
    }
}