[Design Pattern] Adapter Pattern

One-line pattern summary

A pattern that converts an incompatible existing interface into the interface expected by the current system.

Typical Unity use cases

• When aligning a legacy or external SDK with the project’s standard API.
• When reusing an existing implementation without modifying it.

Parts (roles)

• Target
• Adaptee
• Adapter

Unity example (C#)

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

public interface IAdsService
{
    void ShowRewardedAd(string placementId);
}

public sealed class LegacyAdsSdk
{
    public void ShowRewardVideo(string zoneId) { }
}

public sealed class LegacyAdsServiceAdapter : IAdsService
{
    private readonly LegacyAdsSdk legacyAdsSdk = new();

    public void ShowRewardedAd(string placementId)
    {
        legacyAdsSdk.ShowRewardVideo(placementId);
    }
}

Advantages

• It clarifies module boundaries and reduces coupling.
• Features can be extended or integrated without modifying existing code.

Things to watch out for

• If wrapper layers become too deep, debugging gets harder.
• Interfaces should stay small so responsibility boundaries do not blur.

Interaction diagram

This shows the flow where an existing interface is converted into the target interface for reuse.

flowchart LR

  client["Game UI"]
  target["ILeaderboardService"]
  adapter["LeaderboardAdapter"]
  adaptee["Legacy SDK"]
  result["Rank Data"]

  client -- "GetTopRanks()" --> target
  target --> adapter
  adapter -->|Convert Call| adaptee
  adaptee -->|legacy response| adapter
  adapter -->|mapped DTO| result
  result --> client