Generating Code with ISourceWriter #

This code was originally written and proven out in the related Marten and described in a post titled Using Roslyn for Runtime Code Generation in Marten. This code was ripped out of Marten itself, but it's happily running now in Lamar a couple years later.

Lamar provides the LamarCodeGeneration.ISourceWriter service -- and a lot of related extension methods -- to help write common code constructs and maintain legible code indention just like you'd use if you were writing the code in an editor or IDE.

The Basics #

To dip our toes into source generation, let's write a simple method to a string that would just write out "Hello" to the console:

var writer = new SourceWriter();

writer.Write(@"
BLOCK:public void SayHello()
Console.WriteLine('Hello');
END
".Replace("'", "\""));

Console.WriteLine(writer.Code());

After that code, the value of the SourceWriter.Code() method is this text:

public void Go()
{
    Console.WriteLine("Hello");
}

A few notes on what SourceWriter.Write() is doing:

• Starting a line with BLOCK: tells Lamar to write an open bracket '{' on the next line of code and to increment the leading spaces for subsequent lines
• The Write() method is processing each line in the text one at a time, so the call to Console.WriteLine("Hello") would be indented because it is inside a code block for the method
• The END text tells Lamar to write a closing '}' bracket on the next line, then decrement the leading spaces for the next lines of code

Other basic method usages are shown below:

var writer = new SourceWriter();

// Write an empty line into the code 
writer.BlankLine();

// Writes a single line into the code
// with the proper indention. Does NOT
// respect the BLOCK: and END directives
writer.WriteLine("// A comment");

// Writes a closing '}' character into the 
// next line and decrements the leading space
// indention for the following lines of code
writer.FinishBlock();

Advanced Usages #

Here are some of the advanced usages of ISourceWriter:

var writer = new SourceWriter();

// Add "using [namespace]; statements
writer.UsingNamespace(typeof(Console).Namespace);
writer.UsingNamespace<IOperation>();

writer.Namespace("GeneratedCode");
// Write new classes and code within the namespace
writer.FinishBlock();

// Helper to write using blocks in C# code
writer.UsingBlock("var conn = new SqlConnection()", w =>
{
    w.Write("conn.Open();");
    // other statements
});

// Write a comment text into the code at the correct indention
// level
writer.WriteComment("Some message");

// Start the declaration of a new public class named "MyClass"
// that implements the IDisposable interface
writer.StartClass("MyClass", typeof(IDisposable));