Generic Best Practices

Vaibhav • September 11, 2025

Over the last several articles, we’ve explored the power and flexibility of generics in C#. From generic classes and methods to constraints, collections, delegates, and nested types, generics have proven to be a cornerstone of reusable, type-safe programming. But with great power comes great responsibility. In this article, we’ll walk through the best practices for designing, using, and maintaining generic code-so your solutions stay clean, predictable, and scalable.

Design for Reuse, Not for Everything

Generics are meant to make code reusable across types. But that doesn’t mean every class or method should be generic. Before introducing a type parameter, ask yourself: “Is this logic truly type-independent?” If your method only works with strings, don’t make it generic. If your class only handles numbers, consider using numeric types directly or constrain the generic to numeric interfaces.

// ❌ Over-generic
public class Logger<T>
{
    public void Log(T message) => Console.WriteLine(message);
}

// ✅ Better
public class Logger
{
    public void Log(string message) => Console.WriteLine(message);
}

The first version is generic, but it doesn’t need to be. The second version is simpler and clearer. Use generics only when the type truly varies.

Use Meaningful Type Parameter Names

While T is the conventional name for a single type parameter, it’s not always the best choice. When you have multiple type parameters, use descriptive names like TKey, TValue, TInput, or TResult. This improves readability and helps others understand your intent.

// ✅ Clear and descriptive
public interface IMapper<TInput, TResult>
{
    TResult Map(TInput input);
}

This interface makes it clear that the method maps an input to a result. Avoid cryptic names like X or U unless the context is obvious.

Constrain Type Parameters Thoughtfully

Constraints help you enforce rules on generic types. Use them when your logic depends on specific capabilities-like having a parameterless constructor, implementing an interface, or being a reference type. But don’t over-constrain. Only add constraints when they’re truly needed.

// ✅ Appropriate constraint
public class Repository<T> where T : IEntity, new()
{
    public T Create() => new T();
}

This class requires T to implement IEntity and have a parameterless constructor. That’s justified because it creates instances and accesses IEntity members. Avoid constraints that don’t serve a purpose.

Prefer Generic Interfaces for Abstraction

When designing APIs or frameworks, use generic interfaces to define flexible contracts. This allows consumers to implement the interface with their own types, while preserving type safety. It also enables polymorphism and dependency injection.

public interface IRepository<T>
{
    void Add(T item);
    T Get(int id);
}

This interface can be implemented for User, Product, or any other entity. It’s reusable and clean. Avoid hardcoding types in interfaces unless the behavior is truly type-specific.

Use default(T) Safely

The default keyword is useful for initializing or returning fallback values in generic code. But be cautious-default for reference types is null, and for value types it may not be meaningful. Always validate default values before using them in logic.

public T GetOrDefault<T>(T value)
{
    return value != null ? value : default(T);
}

This method checks for null before falling back to default. It’s safe and predictable. Avoid assuming that default is always valid for your use case.

Avoid Deeply Nested Generic Types

Nested generics are powerful, but they can quickly become unreadable. If you find yourself writing types like List<Dictionary<string, List<Tuple<int, bool>>>>, consider breaking them down or using type aliases. Complex types are harder to debug and maintain.

using ScoreMap = Dictionary<string, List<Tuple<int, bool>>>;

List<ScoreMap> data = new List<ScoreMap>();

This alias simplifies the type and makes your code more readable. Use helper methods or classes to encapsulate complexity when needed.

Leverage Type Inference

C# supports type inference for generic methods, delegates, and lambdas. Let the compiler do the work when the context is clear. This reduces verbosity and improves readability.

public static T Echo<T>(T input) => input;

var result = Echo("Hello"); // T is inferred as string

You don’t need to specify T explicitly-the compiler infers it from the argument. But if inference fails or makes the code unclear, specify the type manually.

Use Built-in Generic Delegates

C# provides built-in generic delegates like Func, Action, and Predicate. Use them for common patterns instead of defining custom delegates. They’re well-known, expressive, and integrate seamlessly with LINQ and events.

Func<int, int> square = x => x * x;
Action<string> greet = name => Console.WriteLine($"Hello, {name}!");
Predicate<int> isEven = x => x % 2 == 0;

These delegates cover most use cases. Define custom delegates only when you need a more descriptive name or a specialized signature.

Document Generic Behavior Clearly

Generic code can be harder to understand, especially for beginners. Use XML comments or inline documentation to explain what the type parameters represent, what constraints apply, and how the method or class behaves.

/// <summary>Maps an input value to a result.</summary>
/// <typeparam name="TInput">The type of input.</typeparam>
/// <typeparam name="TResult">The type of result.</typeparam>
public interface IMapper<TInput, TResult>
{
    TResult Map(TInput input);
}

This documentation helps consumers understand how to use the interface correctly. It’s especially important in public APIs and shared libraries.

Test Generic Code Thoroughly

Generic code is flexible, but that means it can behave differently depending on the type. Write unit tests for multiple type scenarios-reference types, value types, nullable types, and custom types. This ensures your logic holds up across use cases.

[TestMethod]
public void TestEchoWithInt()
{
    Assert.AreEqual(42, Echo(42));
}

[TestMethod]
public void TestEchoWithString()
{
    Assert.AreEqual("Hello", Echo("Hello"));
}

These tests validate that Echo works for both int and string. Cover edge cases like null, default, and empty collections.

Avoid Boxing and Unboxing

One of the benefits of generics is avoiding boxing and unboxing for value types. But if you use object or non-generic collections, you lose that benefit. Stick to generic types to preserve performance and type safety.

// ❌ Boxing
ArrayList list = new ArrayList();
list.Add(42); // Boxed

// ✅ No boxing
List<int> list = new List<int>();
list.Add(42);

The second version is faster and safer. Avoid object unless you truly need to store mixed types.

Summary

Generics are a powerful feature in C#, enabling reusable, type-safe code across classes, methods, interfaces, and delegates. But to use them effectively, you need to follow best practices. Design for true type independence, use meaningful type names, constrain thoughtfully, and document clearly. Leverage built-in delegates, type inference, and nested structures wisely. Avoid over-complication, test thoroughly, and stay within the boundaries of what generics are meant to solve. With these practices, your generic code will be robust, readable, and ready for real-world applications. In the next article, we’ll explore Reflection with Generics-how to inspect and manipulate generic types at runtime using the powerful reflection API.