「EntityはIDを持ってるよね」をprotocolで表現し、Entity.IDを定義不要にする

EntityID.swift

protocol Entity {
    associatedtype RawIDValue: Hashable
    typealias ID = EntityID<Self>
}

struct EntityID<E: Entity>: RawRepresentable, Hashable {
    let rawValue: E.RawIDValue
}
extension EntityID {
    init(_ value: E.RawIDValue) {
        rawValue = value
    }
}

struct Hoge: Entity, Equatable {
    typealias RawIDValue = String

    let id: ID
    let name: String
}
let hogeID = Hoge.ID("id_a")
let hoge1 = Hoge(id: .init("id_a"), name: "田中")
let hoge2 = Hoge(id: .init("id_b"), name: "田中")
let hoge3 = Hoge(id: .init("id_b"), name: "鈴木")
print(hoge1.id == hogeID)   // true
print(hoge1.id == hoge2.id) // false
print(hoge2.id == hoge3.id) // true
print(hoge2 == hoge3)       // false

struct Fuga: Entity {
    typealias RawIDValue = Int
    let id: ID
}
struct Piyo: Entity {
    typealias RawIDValue = Int
    let id: ID
}
let fugaID = Fuga.ID(1)
let piyoID = Piyo.ID(1)
//print(fugaID == piyoID)
// 👆Error: Binary operator '==' cannot be applied to operands of type 'Fuga.ID' (aka 'EntityID<Fuga>') and 'Piyo.ID' (aka 'EntityID<Piyo>')