DEV Community: Wobby

Why Multiple Inheritance Is Usually Bad: The Diamond Problem Explained Through Naruto's Edo Tensei

Wobby — Wed, 03 Sep 2025 17:15:02 +0000

Multiple inheritance sounds powerful but often leads to dangerous ambiguity. Let's see why with Naruto's Edo Tensei.

The Anime Hook: Edo Tensei's Conflicted Ninja

Imagine Orochimaru resurrects a ninja who trained under two masters, Jiraiya and Tsunade. Both taught a technique called useUltimateJutsu(), but each technique is completely different.

Who wins when the Edo Tensei ninja tries to use useUltimateJutsu()? This conflict is the heart of the famous Diamond Problem in programming.

What Is the Diamond Problem?

The Diamond Problem happens when a class inherits from two parents who both inherit from the same grandparent—and the parents override the same method. The child inherits that method twice, causing ambiguity on which one to run.

Here's a simplified diamond shape:

      BaseNinja
         /       \
    Jiraiya     Tsunade
         \       /
      EdoShinobi

Both Jiraiya and Tsunade override useUltimateJutsu() from BaseNinja. Which one does EdoShinobi use?

Diamond Problem In Code (Mixin Simulation)

TypeScript forbids direct multiple class inheritance, but mixins can simulate it. Here's the pitfall:

class BaseNinja {
  constructor(public name: string) {}

  useUltimateJutsu() {
    console.log(`${this.name} uses the basic ultimate technique`)
  }
}

function JiraiyaTraining<T extends new (...args: any[]) => BaseNinja>(Base: T) {
  return class extends Base {
    useUltimateJutsu() {
      console.log(`${this.name} uses Rasengan! 🌀`)
    }
  }
}

function TsunadeTraining<T extends new (...args: any[]) => BaseNinja>(Base: T) {
  return class extends Base {
    useUltimateJutsu() {
      console.log(`${this.name} uses Cherry Blossom Impact! 🌸`)
    }
  }
}

class EdoShinobi extends TsunadeTraining(JiraiyaTraining(BaseNinja)) {}

const edo = new EdoShinobi('Minato (Edo)')
edo.useUltimateJutsu()
// Output: Minato (Edo) uses Cherry Blossom Impact! 🌸
// Jiraiya's Rasengan is silently overwritten and lost

The last mixin applied wins, silently overriding previous methods — a classic Diamond Problem trap.

Clean Solution: Composition

Instead of inheritance, use composition - the ninja has a list of masters to ask when performing techniques:

interface JutsuMaster {
  teachUltimate(name: string): void
}

class Jiraiya implements JutsuMaster {
  teachUltimate(name: string) {
    console.log(`${name} learns Rasengan from Jiraiya! 🌀`)
  }
}

class Tsunade implements JutsuMaster {
  teachUltimate(name: string) {
    console.log(`${name} learns Cherry Blossom Impact from Tsunade! 🌸`)
  }
}

class EdoShinobi {
  private masters: JutsuMaster[] = []

  constructor(public name: string) {}

  addMaster(master: JutsuMaster) {
    this.masters.push(master)
  }

  useAllTechniques() {
    this.masters.forEach(master => master.teachUltimate(this.name))
  }
}

const edo = new EdoShinobi('Minato (Edo)')
edo.addMaster(new Jiraiya())
edo.addMaster(new Tsunade())
edo.useAllTechniques()
// Output:
// Minato (Edo) learns Rasengan from Jiraiya! 🌀
// Minato (Edo) learns Cherry Blossom Impact from Tsunade! 🌸

Composition lets you use all techniques explicitly, avoiding ambiguity.

Why Most Languages Avoid Multiple Inheritance

The Diamond Problem causes ambiguous, fragile code
Maintenance and testing suffer
Alternative patterns (composition, interfaces, strategy) are clearer and safer

Treat multiple inheritance like Edo Tensei: tempting but forbidden for a reason.

TypeScript Design Patterns: When Anime Accidentally Teaches You To Code

Wobby — Fri, 23 May 2025 03:58:32 +0000

TypeScript Design Patterns: When Anime Accidentally Teaches You To Code

Ever notice how your favorite anime moments follow the exact same patterns as good software design? That's not a coincidence.

Before We Start: What You Need

Prerequisites: Solid JavaScript/TypeScript basics (classes, interfaces, OOP). If you're still figuring out const vs let, hit the official TypeScript docs first.

The Promise: By the end, you'll see code patterns everywhere in anime - and remember them forever because of it.

1. Observer Pattern: Death Note's Notification System

Picture this: Light writes a name in the Death Note. Instantly, every shinigami in the death realm gets notified. Ryuk starts laughing, the death registry updates, other death gods take notes. One action, multiple reactions - all happening automatically.

That's the Observer pattern in its purest form.

interface ShinigamiObserver {
  onDeath(victim: string, cause: string): void
}

class DeathNote {
  private observers = new Set<ShinigamiObserver>()

  subscribe(shinigami: ShinigamiObserver) {
    this.observers.add(shinigami)
  }

  unsubscribe(shinigami: ShinigamiObserver) {
    this.observers.delete(shinigami)
  }

  writeVictim(name: string, cause: string = 'heart attack') {
    console.log(`📓 '${name}' written in Death Note...`)

    this.observers.forEach(observer => {
      try {
        observer.onDeath(name, cause) // ✅ Fixed: was 'victim', now 'name'
      } catch (err) {
        console.error('⚠️ Shinigami observation failed:', err)
      }
    })
  }
}

class Ryuk implements ShinigamiObserver {
  onDeath(victim: string, cause: string) {
    console.log(`🍎 Ryuk chuckles: 'Humans are so entertaining...'`)
  }
}

class DeathRegistry implements ShinigamiObserver {
  onDeath(victim: string, cause: string) {
    console.log(`📋 Registry updated: ${victim} - ${cause}`)
  }
}

// Usage
const deathNote = new DeathNote()
deathNote.subscribe(new Ryuk())
deathNote.subscribe(new DeathRegistry())
deathNote.writeVictim('L', 'heart attack')

Why This Matters In Real Code:

Event systems: Button clicks, API responses, WebSocket messages
Model-view updates: React state changes triggering multiple component re-renders
Notification systems: User actions triggering emails, push notifications, and analytics

When NOT to use: Simple one-to-one relationships, performance-critical loops (observer iteration overhead).
Testing reality: Easy to mock observers and verify they receive events, but debugging cascading updates when observers trigger more events is absolute hell.

2. Strategy Pattern: Pokemon Type Effectiveness

Pokemon don't hardcode damage calculations. Charizard doesn't have an if (enemy === 'grass') damage *= 2 buried somewhere in its attack method. Instead, it has a Fire Strategy that knows how to handle all type matchups.

When Arceus changes types with different plates? Same Pokemon, different strategy object. Clean, swappable, testable.

interface ElementalStrategy {
  calculateDamage(basePower: number, targetType: string): number
}

class FireStrategy implements ElementalStrategy {
  private effectiveness = {
    grass: 2.0,
    water: 0.5,
    fire: 0.5,
    normal: 1.0
  }

  calculateDamage(basePower: number, targetType: string): number {
    const multiplier = this.effectiveness[targetType] || 1.0
    return basePower * multiplier
  }
}

class WaterStrategy implements ElementalStrategy {
  private effectiveness = {
    fire: 2.0,
    grass: 0.5,
    water: 0.5,
    normal: 1.0
  }

  calculateDamage(basePower: number, targetType: string): number {
    const multiplier = this.effectiveness[targetType] || 1.0
    return basePower * multiplier
  }
}

class Pokemon {
  constructor(
    private name: string,
    private elementalStrategy: ElementalStrategy
  ) {}

  changeType(newStrategy: ElementalStrategy) {
    this.elementalStrategy = newStrategy
    console.log(`${this.name} changed type!`)
  }

  attack(targetType: string, movePower: number = 50) {
    const damage = this.elementalStrategy.calculateDamage(movePower, targetType)
    console.log(`${this.name} deals ${damage} damage!`)
    return damage
  }
}

const charizard = new Pokemon('Charizard', new FireStrategy())
charizard.attack('grass')
charizard.attack('water')

charizard.changeType(new WaterStrategy())
charizard.attack('fire')

Real-World Power:

Payment processing: PayPal vs Stripe vs credit card - same checkout flow, different payment strategies
A/B testing: Swap recommendation algorithms without changing the product page
Data sorting: QuickSort vs MergeSort vs HeapSort based on data size

Skip it when: You only have 1-2 variants (total overkill), or algorithms need to share complex internal state.
Testing reality: Each strategy tests in isolation - absolutely beautiful for unit tests. You can inject mock strategies for testing edge cases.

3. Command Pattern: JoJo Stand Abilities

Every Stand ability is literally a Command object! Star Platinum's "ORA ORA" rush? That's a command with execute(). Crazy Diamond's restoration? Command with both execute() and undo(). Gold Experience's life creation? Another command.

Jotaro doesn't directly punch things - he queues up ORA commands and Star Platinum executes them in sequence.

interface StandCommand {
  execute(): void
  undo?(): void
  priority?: number
}

class OraPunch implements StandCommand {
  priority = 1
  constructor(private target: string, private damage: number) {}

  execute() {
    console.log(`⭐ ORA! Star Platinum punches ${this.target} for ${this.damage} damage!`)
  }
}

class CrazyRestore implements StandCommand {
  priority = 2
  private restored = false

  constructor(private target: string) {}

  execute() {
    console.log(`💎 DORA! Crazy Diamond restores ${this.target}!`)
    this.restored = true
  }

  undo() {
    if (this.restored) {
      console.log(`💥 ${this.target} breaks again!`)
      this.restored = false
    }
  }
}

class StandUser {
  private commandQueue: StandCommand[] = []
  private executedCommands: StandCommand[] = []

  queueAbility(command: StandCommand) {
    this.commandQueue.push(command)
    this.commandQueue.sort((a, b) => (b.priority || 0) - (a.priority || 0))
  }

  executeAll() {
    this.commandQueue.forEach(cmd => {
      cmd.execute()
      this.executedCommands.push(cmd)
    })
    this.commandQueue = []
  }

  undoLast() {
    const lastCommand = this.executedCommands.pop()
    if (lastCommand?.undo) {
      lastCommand.undo()
    }
  }
}

const josuke = new StandUser()
josuke.queueAbility(new OraPunch('Angelo', 50))
josuke.queueAbility(new CrazyRestore('broken wall'))
josuke.executeAll() // Restoration happens first (higher priority)
josuke.undoLast()   // Wall breaks again!

Real-World Applications:

Undo/redo systems: Text editors, image editors, any app with Ctrl+Z
Macro recording: Recording user actions and replaying them
GUI actions: Button clicks become command objects for easier testing
Database transactions: Each operation as a command, rollback via undo

Skip it when: Simple direct method calls, memory-constrained environments (commands create lots of objects).
Testing reality: Absolutely fantastic for testing - verify commands were created correctly without executing them. Test undo logic separately from execution logic.

4. Factory Pattern: Naruto Summoning Contracts

Nobody manually creates Gamabunta or Manda with new GiantToad(). You perform the summoning jutsu (factory method) and the appropriate creature appears based on your contract (registry) and chakra level.

The factory handles all the complex logic: "Does this ninja have a toad contract? How much chakra do they have? Create the right size summon."

abstract class SummonedCreature {
  abstract size: 'small' | 'medium' | 'boss'
  abstract attack(): void
  abstract element: string
}

class Gamabunta extends SummonedCreature {
  size = 'boss'
  element = 'water'

  attack() {
    console.log('🐸 Gamabunta spits a massive water bullet!')
  }
}

class Gamakichi extends SummonedCreature {
  size = 'medium'
  element = 'water'

  attack() {
    console.log('🐸 Gamakichi launches water shuriken!')
  }
}

class Manda extends SummonedCreature {
  size = 'boss'
  element = 'earth'

  attack() {
    console.log('🐍 Manda burrows and strikes from underground!')
  }
}

class SummoningContractFactory {
  private contracts: Record<string, Array<new () => SummonedCreature>> = {}

  constructor() {
    this.contracts.toad = [Gamakichi, Gamabunta]
    this.contracts.snake = [Manda]
  }

  signContract(animal: string, creatures: Array<new () => SummonedCreature>) {
    this.contracts[animal] = creatures
  }

  summon(contract: string, chakraLevel: 'low' | 'medium' | 'high'): SummonedCreature {
    const availableCreatures = this.contracts[contract]
    if (!availableCreatures?.length) {
      throw new Error(`No ${contract} contract signed!`)
    }

    const sizeMap = { low: 'small', medium: 'medium', high: 'boss' }
    const targetSize = sizeMap[chakraLevel]

    const CreatureClass = availableCreatures.find(CreatureClass => {
      const temp = new CreatureClass()
      return temp.size === targetSize
    }) || availableCreatures[0]

    return new CreatureClass()
  }
}

const naruto = new SummoningContractFactory()
const gamabunta = naruto.summon('toad', 'high')
gamabunta.attack()

class Katsuyu extends SummonedCreature {
  size = 'boss'
  element = 'healing'
  attack() {
    console.log('🐌 Katsuyu releases healing acid!')
  }
}
naruto.signContract('slug', [Katsuyu])

Factory Power In Real Apps:

Database connections: MySQL vs PostgreSQL vs MongoDB - same interface, different implementations
HTTP clients: Axios vs Fetch vs custom - factory picks based on environment
UI components: Button factory that creates iOS vs Android vs Web buttons
Plugin systems: Load different payment processors, authentication providers, etc.

Don't use when: Simple object creation, only one type of object, tight coupling is actually fine.
Testing reality: Tricky because factories hide construction details. Use dependency injection to pass in mock factories for testing.

5. Singleton Pattern: One Piece Devil Fruit Powers

Here's the thing about Devil Fruits: each power can only exist once in the entire world. When Luffy eats the Gomu Gomu fruit, nobody else can have rubber powers until he dies and the fruit respawns somewhere else.

That's Singleton pattern - enforcing "only one instance can exist."

class DevilFruit {
  private static activePowers = new Map<string, DevilFruit>()

  constructor(private powerName: string, private user: string) {
    if (DevilFruit.activePowers.has(powerName)) {
      const currentUser = DevilFruit.activePowers.get(powerName)?.user
      throw new Error(`${powerName} power already belongs to ${currentUser}!`)
    }

    DevilFruit.activePowers.set(powerName, this)
    Object.freeze(this)
    console.log(`🍎 ${user} gained ${powerName} powers!`)
  }

  use() {
    console.log(`${this.user} uses ${this.powerName}!`)
  }

  static releasePower(powerName: string) {
    if (DevilFruit.activePowers.delete(powerName)) {
      console.log(`💀 ${powerName} power is available again...`)
    }
  }

  static getActivePowers() {
    return Array.from(DevilFruit.activePowers.entries()).map(
      ([power, fruit]) => `${power}: ${fruit.user}`
    )
  }
}

const luffyPower = new DevilFruit('Gomu Gomu', 'Luffy')
luffyPower.use()

try {
  const fakeLuffy = new DevilFruit('Gomu Gomu', 'Fake Luffy')
} catch (e) {
  console.log(e.message) // "Gomu Gomu power already belongs to Luffy!"
}

DevilFruit.releasePower('Gomu Gomu')
const newUser = new DevilFruit('Gomu Gomu', 'Someone New')

Legitimate Singleton Use Cases:

Database connection pools: Expensive to create, should be shared
Logging systems: One logger instance for the entire app
Configuration objects: App settings that should be globally accessible
Cache managers: One cache instance to rule them all

Skip it when: Most of the time! Creates hidden dependencies, makes testing a nightmare, breaks inversion of control.
Testing reality: Absolutely terrible - global state makes tests interdependent and impossible to parallelize. Consider dependency injection instead.

6. Template Method Pattern: Shounen Training Arcs

Every shounen training arc follows the exact same structure: Hero arrives → meets mentor → struggles with impossible training → has dramatic breakthrough → powers up → leaves to fight the real enemy.

Dragon Ball, Naruto, Bleach, One Piece - they all use this template. The steps never change, but the specific details are wildly different.

abstract class TrainingArc {
  complete() {
    this.arrive()
    this.meetMentor()
    this.struggle()
    this.breakthrough()
    this.powerUp()
    this.depart()
  }

  protected arrive() {
    console.log('🚶 Hero arrives at mysterious training location...')
  }

  protected meetMentor() {
    console.log('👴 A wise but eccentric mentor appears...')
  }

  protected abstract struggle(): void

  protected abstract breakthrough(): void

  protected powerUp() {
    console.log('✨ Power level increases dramatically!')
  }

  protected depart() {
    console.log('🏃 Time to test new powers against the real enemy!\n')
  }
}

class DragonBallTraining extends TrainingArc {
  protected struggle() {
    console.log('💪 Goku trains under 100x Earth gravity!')
    console.log('😤 Body gets crushed repeatedly, bones breaking...')
  }

  protected breakthrough() {
    console.log('⚡ Goku\'s hair turns golden - Super Saiyan achieved!')
    console.log('💥 I am the hope of the universe!')
  }
}

class NarutoTraining extends TrainingArc {
  protected struggle() {
    console.log('🌀 Naruto fails to form Rasengan 1000+ times...')
    console.log('😓 Hands get shredded from chakra control mistakes...')
  }

  protected breakthrough() {
    console.log('🌪️ Perfect Rasengan forms in Naruto\'s palm!')
    console.log('🦊 I never go back on my word - that\'s my ninja way!')
  }
}

class BleachTraining extends TrainingArc {
  protected struggle() {
    console.log('⚔️ Ichigo fights his inner Hollow for days...')
    console.log('👹 Dark Ichigo taunts him mercilessly...')
  }

  protected breakthrough() {
    console.log('🎭 Ichigo masters his Hollow mask!')
    console.log('💀 I\'ll protect everyone with my own power!')
  }
}

console.log('=== Dragon Ball Training Arc ===')
new DragonBallTraining().complete()

console.log('=== Naruto Training Arc ===')
new NarutoTraining().complete()

console.log('=== Bleach Training Arc ===')
new BleachTraining().complete()

Template Method In Real Development:

Data processing pipelines: Load → validate → transform → save (details vary per data type)
Authentication flows: Check credentials → validate permissions → grant access (OAuth vs JWT vs API keys)
Testing frameworks: Setup → run test → cleanup → report (Jest, Mocha, etc.)
Build processes: Compile → bundle → optimize → deploy (different for each framework)

Skip it when: Highly dynamic workflows where steps change based on runtime conditions, or when inheritance feels forced.
Testing reality: Excellent - test the template separately from implementations, and test each step in isolation. Easy to mock specific steps.

The Big Picture: Why These 6 Patterns Rule

These aren't random patterns picked from a textbook - they're the essential toolkit that covers 80% of real design problems you'll face:

Observer: When one thing needs to tell many things (events, notifications)
Strategy: When you need swappable algorithms (payment methods, sorting algorithms)
Command: When actions become objects (undo/redo, macros, queuing)
Factory: When creation gets complex (database connections, plugins)
Singleton: When you truly need "only one" (rarely, but sometimes legitimately)
Template Method: When steps stay the same but details change (workflows, pipelines)

Notice how they complement each other? You might use a Factory to create different Strategies, then queue them up as Commands, with Observers listening for results - all within a Template Method workflow.

Your Next Steps: From Anime Fan to Pattern Master

Pick the pattern that clicked hardest - which anime example made you go "holy shit, that's brilliant"?
Find it in your current codebase - I guarantee it's already there, just implemented messily with if/else chains or copy-pasta code.
Refactor one small piece using the pattern properly - don't boil the ocean, just clean up one method or class.
Feel the difference in code clarity, testability, and maintainability - once you experience clean pattern usage, you can't go back.
Start seeing patterns everywhere - in other anime, in your daily apps, in frameworks you use. They're literally everywhere once your brain is trained to spot them.

The goal isn't to force patterns into every line of code - it's to recognize when you're solving the same fundamental problems that anime characters face, just in TypeScript instead of chakra and Stand battles.

Additional Resources:

Refactoring Guru Design Patterns - Best visual explanations
TypeScript Official Docs - Master the fundamentals first
MDN JavaScript Guide - Core language concepts
GeeksforGeeks TypeScript Patterns - More examples
FreeCodeCamp Design Patterns - Free deep dives

Now go forth and code something legendary - your favorite anime heroes would be proud! 🚀