こういう実装はありなんだろうか。 #swift #CodePiece

CodePiece.swift

struct Permission<Holder: PermissionHolder> {
    let holder: Holder
}

protocol PermissionHolder {
    var can: Permission<Self> { get }
}

extension PermissionHolder {
    var can: Permission<Self> { return Permission(holder: self) }
}

struct User: PermissionHolder {
    let id: Int64
}

struct Answer {
    let userID: Int64
}

extension Permission where Holder == User {
    func delete(_ answer: Answer) -> Bool {
        return holder.id == answer.userID
    }
}

let user = User(id: 1)
let answer1 = Answer(userID: 1)
user.can.delete(answer1)    // true
let answer2 = Answer(userID: 2)
user.can.delete(answer2)    // false