"Partial Classes"

// File: ExampleClass.Alpha.cs

public partial class ExampleClass {
	public void DoAlphaOne() { ... }
	
	public void DoAlphaTwo() { ... }
}





// File: ExampleClass.Beta.cs

public partial class ExampleClass {
	public void DoBetaOne() { ... }
	
	public void DoBetaTwo() { ... }
}




// Elsewhere

static void Test() {
	var ec = new ExampleClass();
	
	ec.DoAlphaOne();
	ec.DoBetaTwo();
	// etc
}


Code snippet taken from "Two Decades of C#: A Reference - C# 2, 3 and 4".