unity-pattern-dependency-injection

name	unity-pattern-dependency-injection
description	Dependency Injection
category	unity
source	unity-design-patterns-skills
source_path	patterns/dependency-injection/SKILL.md

Dependency Injection

Purpose

Provide collaborators from outside the object so construction, ownership, and substitution stay explicit.

Use When

• Scene lookups or singletons are hiding dependencies.
• Services should be replaceable in tests.
• Bootstrap code can own wiring decisions.

Avoid When

• The feature is tiny and extra wiring adds more cost than clarity.
• A service locator is being used as fake DI.

Unity Implementation Recipe

1. Identify real collaborators.
2. Inject them at construction or initialization boundaries.
3. Keep wiring in a composition root.
4. Use interfaces only where substitution matters.

Common Pitfalls

• Mixing DI with hidden globals.
• Injecting after runtime logic already started.

Minimal Unity Sketch

public sealed class QuestPresenter
{
    private readonly IQuestRepository _quests;
    private readonly IClock _clock;

    public QuestPresenter(IQuestRepository quests, IClock clock)
    {
        _quests = quests;
        _clock = clock;
    }
}

Response Shape

• Say whether Dependency Injection is actually the right fit.
• Map it to concrete Unity types, ownership, and lifecycle.
• Prefer a production-shaped skeleton over a long tutorial dump.
• Call out the simpler alternative if this pattern would be overengineering.