Pokemon Type Erasure (take 2)

pokemon.swift

//: Second Type Erasure

import Foundation

protocol Pokemon {
    typealias Power
    func attack(power: Power)
}

private class _AnyPokemonBoxBase<Power>: Pokemon {
    func attack(power: Power) {
        fatalError()
    }
}

private class _AnyPokemonBox<P: Pokemon>: _AnyPokemonBoxBase<P.Power> {
    typealias Power = P.Power
    let base: P
    init(_ base: P) {
        self.base = base
    }
    override func attack(power: Power) {
        base.attack(power)
    }
}

final class AnyPokemon<Power>: Pokemon {
    private let box: _AnyPokemonBoxBase<Power>
    
    init<P: Pokemon where P.Power == Power>(_ base: P) {
        self.box = _AnyPokemonBox(base)
    }
    func attack(power: Power) {
        box.attack(power)
    }
}

struct Electric {
    var charge: Int = 0
    func spark() {
        print("Spark: ", Array(count: charge, repeatedValue: "⚡️").joinWithSeparator(""))
    }
}

class Pikachu : Pokemon {
    func attack(power: Electric) {
        power.spark()
    }
}

struct Fire {
    var level: Int = 0
    func blast() {
        print("Blast: ", Array(count: level, repeatedValue: "🔥").joinWithSeparator(""))
    }
}

class Charmander: Pokemon {
    func attack(power: Fire) {
        power.blast()
    }
}

class Raichu: Pokemon {
    func attack(power: Electric) {
        power.spark()
    }
}

let pikachu = AnyPokemon(Pikachu())
let charmander = AnyPokemon(Charmander())
let raichu = AnyPokemon(Raichu())

pikachu.attack(Electric(charge: 20))
charmander.attack(Fire(level: 10))
let pokemons: [AnyPokemon<Electric>] = [pikachu, raichu]