Code Generation For Auto-Implemented Properties

I recently ventured into one of the more obscure areas of .NET framework - code generation. The project involved rules engine manipulating properties of our internal domain objects. Long story short, I had to create a routine that converts our domain objects into .NET classes (derived from System.Workflow.Activity). These generated classes did not have much behavior - all methods were pushed to the base class - but they did carry so many properties that they in turn had to be grouped together into classes.

Writing code generation logic for a property turned out to be a lot of work: first, I had to add declaration for a private backing field, then a property declaration, including code expressions for both getter and setter. Here's sample code similar to what I ended up with:

var myType = new CodeTypeDeclaration("Person");

var field = new CodeMemberField()

{

    Name = "_LastName",

    Type = new CodeTypeReference("System.String"),

    Attributes = MemberAttributes.Private

};

myType.Members.Add(field);

var prop = new CodeMemberProperty()

{

    Name = "LastName",

    Type = new CodeTypeReference("System.String"),

    Attributes = MemberAttributes.Public

};

prop.GetStatements.Add(

    new CodeMethodReturnStatement(

        new CodeFieldReferenceExpression(

            new CodeThisReferenceExpression(), "_LastName")));

prop.SetStatements.Add(

    new CodeAssignStatement(

        new CodeFieldReferenceExpression(

            new CodeThisReferenceExpression(), "_LastName"), 

        new CodePropertySetValueReferenceExpression()));

myType.Members.Add(prop);

And here is the code that was generated by the above fragment:

private string _LastName;

public string LastName

{

    get { return _LastName; }

    set { _LastName = value; }

}

Of course, C# 3.0 has introduced a much shorted way of declaring the same property: "public string LastName { get; set; }". This syntax is called "auto-implemented properties" and it puts the burden on the compiler to create a backing field and implement getter and setter logic. Naturally, I wanted generated classes to look cleaner, so being an optimist that I am I decided to change code generation logic to create auto-implemented properties instead.

That proved to be a mistake: after a while I realized that classes in System.CodeDom namespace do not support auto-implemented properties generation. The best I could come up with was a hack using CodeSnippetTypeMember:

var snippet = new CodeSnippetTypeMember("public string LastName { get; set; }");

myType.Members.Add(snippet);

This solution is pretty far from ideal. It goes against the spirit of code generation because it allows me to target just one programming language, C#. Still, it is pragmatic. Hopefully, Microsoft can bring CodeDom up to date in a future release.