Generics and Constraints

Advanced Generics and Constraints in C# Programming Tutorial. Deep dive with production-oriented examples—not a shallow overview.

Architecture & mental model

Generics let you write algorithms once (lists, repositories, validators) while keeping compile-time type safety. Constraints (where T : class, new(), interfaces) document what a type parameter must support.

Implementation (production-style)

Type the code below; change names and types to match your domain. Compare with how C# / .NET teams structure layers in mature codebases.

public interface IRepository where T : class
{
    Task GetByIdAsync(int id, CancellationToken ct = default);
    Task AddAsync(T entity, CancellationToken ct = default);
}

public class EfRepository : IRepository where T : class
{
    private readonly DbContext _db;
    public EfRepository(DbContext db) => _db = db;

    public Task GetByIdAsync(int id, CancellationToken ct = default) =>
        _db.Set().FindAsync(new object[] { id }, ct).AsTask();
}

Contrast: common anti-patterns

// Generic method with constraint
public static T Max(T a, T b) where T : IComparable
    => a.CompareTo(b) >= 0 ? a : b;

Decision checklist

• Requirements: What are latency, consistency, and security needs for "Generics and Constraints"?
• Boundaries: Which layer owns this logic (UI, API, domain, infrastructure)?
• Failure modes: What happens when dependencies time out or return partial data?
• Observability: What logs or metrics prove this feature works in production?

Hands-on lab (45–60 min)

1. Reproduce the primary example for "Generics and Constraints" in a scratch project using C# / .NET.
2. Add one automated test (unit or integration) that would fail if you break the core behavior.
3. Introduce a deliberate bug (wrong lifetime, missing await, wrong dependency order) and observe the symptom.
4. Document one trade-off you would present in a design review.

Pitfalls senior engineers avoid

• Over-generic APIs that hurt readability.
• Using generics when a simple interface suffices.
• Boxing value types in non-generic collections.

Interview depth

Question: Explain Generics and Constraints to a junior developer in 2 minutes, then list two trade-offs.

Strong answer: Start with the problem it solves, describe one real project usage, mention a failure you debugged or would test for, and close with alternatives (when not to use this approach).

Summary

You completed an advanced treatment of Generics and Constraints. Revisit after building a feature that uses it end-to-end; spaced repetition with real code beats re-reading alone.