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:
Drawbacks:
Slower execution
More memory usage
Source Generators
Compile-Time Generation
↓
Better Performance
Benefits:
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:
These frameworks use compile-time generation to improve performance and developer experience.
Performance Benefits
Because code is generated during compilation:
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.
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.