Bits of .NET

⚙️ Write Code That Writes Code

Reflection is slow. Source generators run at compile time. Generate JSON serializers, INotifyPropertyChanged, mappers — zero runtime overhead.

📝 Simple Source Generator

[Generator]
public class HelloWorldGenerator : ISourceGenerator
{
    public void Initialize(GeneratorInitializationContext context) { }

    public void Execute(GeneratorExecutionContext context)
    {
        string source = @"
namespace Generated
{
    public static class HelloWorld
    {
        public static void SayHello() => 
            Console.WriteLine("Hello from generated code!");
    }
}";
        context.AddSource("HelloWorld.g.cs", source);
    }
}

// Usage in any project referencing the generator
Generated.HelloWorld.SayHello();

🎯 Real-World: INotifyPropertyChanged

// Attribute
[AttributeUsage(AttributeTargets.Class)]
public class GenerateNotifyPropertyChangedAttribute : Attribute { }

// Generator finds classes with attribute and implements INotifyPropertyChanged
[GenerateNotifyPropertyChanged]
public partial class Person
{
    private string _name;
    public string Name
    {
        get => _name;
        set => SetProperty(ref _name, value);
    }
}

// Generator adds:
// - SetProperty method
// - PropertyChanged event
// - OnPropertyChanged method

💡 Use Cases

• JSON serialization (System.Text.Json source generator)
• Dependency Injection registration
• AutoMapper without reflection
• Regex compilation (RegexGenerator)
• Logging message templates