Compare Lambda Expressions and Anonymous Methods in C#

C# provides multiple ways to define inline functions, primarily through Lambda Expressions and Anonymous Methods. Both approaches allow developers to define and use functions without explicitly declaring a separate method, making code more concise and readable. However, they differ in syntax, usability, and performance considerations.

This post provides an in-depth comparison of Lambda Expressions and Anonymous Methods, including their syntax, use cases, performance considerations, and best practices. By the end, you'll have a clear understanding of when and how to use each approach effectively.

Understanding Anonymous Methods

Anonymous methods were introduced in C# 2.0 to allow inline method definitions without explicitly declaring them. They use the delegate keyword and can be assigned to a delegate type.

Syntax of Anonymous Methods

Here's an example of an Anonymous Method:

using System;

class Program
{
    delegate void PrintMessage(string message);

    static void Main()
    {
        PrintMessage print = delegate (string msg)
        {
            Console.WriteLine(msg);
        };
        
        print("Hello from Anonymous Method");
    }
}

Key Features of Anonymous Methods:

Uses the delegate keyword.
No need to specify a method name.
Can access variables in the enclosing scope (captured variables).
Supports parameter passing like normal methods.

Limitations of Anonymous Methods:

More verbose compared to Lambda Expressions.
Cannot be used with Expression Trees.
Cannot be used in LINQ Queries.

Understanding Lambda Expressions

Lambda Expressions, introduced in C# 3.0, provide a more concise and readable way to define inline functions. They use the => (lambda operator) to separate parameters from the function body.

Syntax of Lambda Expressions

Here's an example of a Lambda Expression:

using System;

class Program
{
    delegate void PrintMessage(string message);

    static void Main()
    {
        PrintMessage print = msg => Console.WriteLine(msg);
        
        print("Hello from Lambda Expression");
    }
}

Key Features of Lambda Expressions:

More concise than Anonymous Methods.
Can be used with Expression Trees.
Fully supported in LINQ Queries.
Implicitly infers parameter types (e.g., msg in the example above).

Expression vs. Statement Lambdas

Lambda expressions come in two forms:

Expression Lambda (Single Expression)

Func<int, int> square = x => x * x;
Console.WriteLine(square(5)); // Output: 25

Statement Lambda (Multiple Statements)

Func<int, int> square = x =>
{
    int result = x * x;
    return result;
};
Console.WriteLine(square(5)); // Output: 25

Key Differences: Lambda Expressions vs. Anonymous Methods

Feature	Lambda Expressions	Anonymous Methods
Syntax	Concise (`=>` operator)	Uses `delegate` keyword
Readability	Easier to read & understand	More verbose
Expression Trees	Supported	Not Supported
LINQ Queries	Fully supported	Not supported
Type Inference	Implicit	Explicit parameter types required
Performance	Generally optimized by compiler	Slightly less optimized
Capturing Variables	Supports closures	Supports closures
Multi-line Functions	Supports both expression & statement lambdas	Supports multi-line statements

When to Use Anonymous Methods

While Lambda Expressions are generally preferred, Anonymous Methods can still be useful in specific cases:

When working with legacy C# 2.0 code where Lambda Expressions are not available.
When you need to explicitly specify the delegate keyword for clarity.
For complex inline functions that require multiple statements and explicit parameter definition.

Example:

delegate void ShowMessage(string message);
ShowMessage show = delegate (string msg)
{
    Console.WriteLine($"Message: {msg}");
};

When to Use Lambda Expressions

Lambda Expressions are the recommended approach in modern C# development. They are best suited for:

LINQ Queries

var numbers = new List<int> { 1, 2, 3, 4, 5 };
var evenNumbers = numbers.Where(n => n % 2 == 0);

Defining Short Inline Functions

Func<int, int> square = x => x * x;

Functional Programming and Delegate-Based API Calls

Action<string> print = msg => Console.WriteLine(msg);

Performance Considerations

While both Anonymous Methods and Lambda Expressions are compiled into similar IL (Intermediate Language) code, there are some differences:

Lambda Expressions are more optimized because they leverage type inference and compiler optimizations.
Anonymous Methods can introduce extra delegate allocations, which may affect performance in high-frequency operations.
Expression Trees allow Lambda Expressions to be converted into data structures, making them more flexible for metaprogramming and query generation.

Example of Expression Trees:

using System;
using System.Linq.Expressions;

class Program
{
    static void Main()
    {
        Expression<Func<int, int>> squareExpression = x => x * x;
        Console.WriteLine(squareExpression);
    }
}

Best Practices

✅ Prefer Lambda Expressions for Modern C# Code

Lambda expressions are shorter, cleaner, and more readable, making them the preferred choice in most cases.

✅ Use Expression Lambdas for Simple Operations

Func<int, int> square = x => x * x;

✅ Use Statement Lambdas for More Complex Logic

Func<int, int> square = x =>
{
    int result = x * x;
    return result;
};

✅ Avoid Anonymous Methods in New Code

Unless working with legacy C# 2.0 code, prefer lambda expressions for better readability and performance.

✅ Use Expression Trees for Dynamic Code Generation

If working with Entity Framework or Expression-Based APIs, use Expression Trees where applicable.

Conclusion

Both Lambda Expressions and Anonymous Methods allow inline function definitions in C#. While Anonymous Methods were an improvement in C# 2.0, Lambda Expressions (introduced in C# 3.0) offer a more concise, readable, and performant way to define inline functions.

Key Takeaways:

Prefer Lambda Expressions in modern C# development.
Anonymous Methods are still valid but largely replaced by lambdas.
Use Lambda Expressions in LINQ, functional programming, and expression trees.
Understand performance implications when using inline functions.

By understanding these differences, you can write cleaner, more efficient, and maintainable C# code!