[Design Pattern] Builder Pattern

One-line pattern summary

A pattern that separates complex object creation into steps to improve readability and safety.

Typical Unity use cases

When creating configuration objects with many options.
When the same process produces different results.

Parts (roles)

Builder
Director (optional)
Product

Unity example (C#)

The code below is a simplified Unity example based on the scenario described above.

public sealed class EnemyWaveConfig
{
    public int EnemyCount;
    public float SpawnIntervalSeconds;
    public string RewardId;
}

public sealed class EnemyWaveBuilder
{
    private readonly EnemyWaveConfig waveConfig = new();

    public EnemyWaveBuilder SetEnemyCount(int enemyCount)
    {
        waveConfig.EnemyCount = enemyCount;
        return this;
    }

    public EnemyWaveBuilder SetSpawnInterval(float spawnIntervalSeconds)
    {
        waveConfig.SpawnIntervalSeconds = spawnIntervalSeconds;
        return this;
    }

    public EnemyWaveBuilder SetReward(string rewardId)
    {
        waveConfig.RewardId = rewardId;
        return this;
    }

    public EnemyWaveConfig Build() => waveConfig;
}

Advantages

Object creation responsibilities are well organized, which makes dependency management easier.
Creation policies can be changed flexibly by environment or situation.

Things to watch out for

Avoid introducing overly abstract creation layers for simple problems.
As creation rules increase, keeping documentation and tests in sync becomes more important.

Interaction diagram

This shows the flow where a complex object is assembled step by step and returned at the end.

flowchart TD

  director["Director"]
  step1["BuildStats()"]
  step2["BuildEquipment()"]
  step3["BuildSkills()"]
  product["CharacterData"]

  director --> step1
  step1 --> step2
  step2 --> step3
  step3 --> product