C# Source Generators: Improving Performance and Reducing Boilerplate Code

Introduction

One of the common challenges in software development is writing repetitive code. Developers often create similar classes, mappings, serialization logic, validation code, and dependency registration code across multiple projects.

Traditionally, these tasks were handled using:

Reflection
Runtime code generation
Manual coding

While effective, these approaches can impact performance and increase maintenance effort.

To address this, Microsoft introduced Source Generators in C# and .NET. Source Generators allow developers to generate code during compilation, reducing boilerplate code while improving application performance.

In this article, you'll learn what Source Generators are, how they work, and practical use cases where they provide real value.

What Are C# Source Generators?

Source Generators are compiler extensions that generate C# source code during the build process.

Instead of creating code at runtime:

Application Starts
      ↓
Generate Code
      ↓
Execute

Source Generators create code during compilation:

Build Project
      ↓
Generate Code
      ↓
Compile
      ↓
Run

The generated code becomes part of the final assembly.

Why Use Source Generators?

Consider a large application containing hundreds of models.

Example:

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
}

You may need:

Validation code
Mapping code
Serialization logic
Dependency registration

Writing this manually becomes repetitive.

Source Generators automate these tasks and reduce development effort.

How Source Generators Work

A Source Generator analyzes source code during compilation and produces additional C# files.

Workflow:

Source Code
      ↓
Compiler
      ↓
Source Generator
      ↓
Generated Code
      ↓
Compiled Assembly

The generated code is available at compile time and requires no runtime generation.

Creating a Simple Source Generator

A Source Generator implements the ISourceGenerator interface.

Example:

[Generator]
public class HelloGenerator
    : ISourceGenerator
{
    public void Execute(
        GeneratorExecutionContext context)
    {
        var source = @"
        public static class GeneratedCode
        {
            public static string Message =>
                ""Hello World"";
        }";

        context.AddSource(
            "GeneratedCode.cs",
            source);
    }

    public void Initialize(
        GeneratorInitializationContext context)
    {
    }
}

During compilation, a new class is automatically generated.

Example Usage

Generated code:

GeneratedCode.Message

Output:

Hello World

The class never existed in the project manually—it was created during the build process.

Source Generators vs Reflection

Many developers compare Source Generators with Reflection.

Reflection

Runtime Inspection
      ↓
Additional Overhead

Benefits:

Flexible
Dynamic

Drawbacks:

Slower execution
More memory usage

Source Generators

Compile-Time Generation
      ↓
Better Performance

Benefits:

Faster execution
Reduced runtime overhead
Better startup performance

For many scenarios, Source Generators are more efficient.

Real-World Use Cases

Automatic Mapping

Applications often map entities to DTOs.

Without generators:

dto.Name = entity.Name;
dto.Price = entity.Price;

Generated mapping code reduces manual work.

Dependency Injection Registration

Large projects may contain dozens of services.

Instead of manually registering:

builder.Services
    .AddScoped<IProductService,
               ProductService>();

A Source Generator can create registrations automatically.

Serialization

Libraries can generate optimized serialization code during compilation instead of relying heavily on reflection.

This improves performance significantly.

Popular Frameworks Using Source Generators

Several modern .NET libraries leverage Source Generators.

Examples include:

System.Text.Json
ASP.NET Core
AutoMapper alternatives
Dependency Injection tools
Logging frameworks

These frameworks use compile-time generation to improve performance and developer experience.

Performance Benefits

Because code is generated during compilation:

Faster application startup
Reduced reflection usage
Lower memory consumption
Improved runtime performance

Example:

Reflection-Based App
      ↓
Higher Startup Cost

Compared to:

Source Generator App
      ↓
Faster Startup

The difference becomes more noticeable in large applications.

Advantages of Source Generators

Source Generators provide several benefits.

Reduced boilerplate code
Better performance
Compile-time validation
Faster startup times
Improved developer productivity
Cleaner codebases

These advantages make them valuable for modern .NET applications.

Common Use Cases

Source Generators are especially useful for:

DTO generation
Object mapping
Dependency registration
Serialization
Validation
Logging helpers
API client generation

Many enterprise applications benefit from these scenarios.

Best Practices

When using Source Generators:

Generate only necessary code.
Keep generators focused on a single purpose.
Avoid generating overly complex code.
Validate generated output.
Document generated behavior clearly.
Monitor build performance.

These practices help maintain a clean development experience.

When Should You Use Source Generators?

Use Source Generators when:

Repetitive code exists.
Reflection impacts performance.
Compile-time validation is beneficial.
Large projects require automation.
Boilerplate code is increasing.

For small projects, the added complexity may not always be necessary.

Conclusion

C# Source Generators are a powerful feature that enables developers to generate code during compilation rather than at runtime. By reducing boilerplate code and minimizing reflection usage, they help improve application performance, startup time, and maintainability.

Whether you're building APIs, enterprise applications, libraries, or cloud-native services, Source Generators can automate repetitive tasks and create cleaner, more efficient codebases. As the .NET ecosystem continues to evolve, Source Generators are becoming an increasingly important tool for modern C# developers.