Compiling code dynamically using C#

Question

How can I wrote C# code to compile and run dynamically generated C# code. Are there examples around?

What I am after is to dynamically build up a C# class (or classe

Answer 1

Two possibilities:

1. Reflection.Emit
2. System.CodeDom.Compiler

---

UPDATE:

As request in the comments section here's a full example illustrating the usage of Reflection.Emit to dynamically build a class and add a static method to it:

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;

public class NotDynamicClass
{
    private readonly List<string> values = new List<string>();

    public void AddValue(string value)
    {
        values.Add(value);
    }

    public void ProcessValues()
    {
        foreach (var item in values)
        {
            Console.WriteLine(item);
        }
    }
}

class Program
{
    public static void Main()
    {
        var assemblyName = new AssemblyName("DynamicAssemblyDemo");
        var assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);
        var moduleBuilder = assemblyBuilder.DefineDynamicModule(assemblyName.Name, false);
        var typeBuilder = moduleBuilder.DefineType("DynamicClass", TypeAttributes.Public);

        var methodBuilder = typeBuilder.DefineMethod(
            "Main",
            MethodAttributes.Public | MethodAttributes.Static,
            null,
            new Type[0]
        );

        var il = methodBuilder.GetILGenerator();
        var ctor = typeof(NotDynamicClass).GetConstructor(new Type[0]);
        var addValueMi = typeof(NotDynamicClass).GetMethod("AddValue");
        il.Emit(OpCodes.Newobj, ctor);
        il.Emit(OpCodes.Stloc_0);
        il.DeclareLocal(typeof(NotDynamicClass));
        il.Emit(OpCodes.Ldloc_0);
        il.Emit(OpCodes.Ldstr, "One");
        il.Emit(OpCodes.Callvirt, addValueMi);
        il.Emit(OpCodes.Ldloc_0);
        il.Emit(OpCodes.Ldstr, "Two");
        il.Emit(OpCodes.Callvirt, addValueMi);
        il.Emit(OpCodes.Ldloc_0);
        il.Emit(OpCodes.Callvirt, typeof(NotDynamicClass).GetMethod("ProcessValues"));
        il.Emit(OpCodes.Ret);
        var t = typeBuilder.CreateType();
        var mi = t.GetMethod("Main");
        mi.Invoke(null, new object[0]);
    }
}

You could put breakpoints inside your not NotDynamicClass methods and see how they get invoked.

---

UPDATE 2:

Here's an example with CodeDom compiler:

using System;
using System.CodeDom.Compiler;
using System.Collections.Generic;
using Microsoft.CSharp;

public class NotDynamicClass
{
    private readonly List<string> values = new List<string>();

    public void AddValue(string value)
    {
        values.Add(value);
    }

    public void ProcessValues()
    {
        foreach (var item in values)
        {
            Console.WriteLine(item);
        }
    }
}

class Program
{
    public static void Main()
    {
        var provider = CSharpCodeProvider.CreateProvider("c#");
        var options = new CompilerParameters();
        var assemblyContainingNotDynamicClass = Path.GetFileName(Assembly.GetExecutingAssembly().Location);
        options.ReferencedAssemblies.Add(assemblyContainingNotDynamicClass);
        var results = provider.CompileAssemblyFromSource(options, new[] 
        { 
@"public class DynamicClass
{
    public static void Main()
    {
        NotDynamicClass @class = new NotDynamicClass();
        @class.AddValue(""One"");
        @class.AddValue(""Two"");
        @class.ProcessValues();
    }
}"
        });
        if (results.Errors.Count > 0)
        {
            foreach (var error in results.Errors)
            {
                Console.WriteLine(error);
            }
        }
        else
        {
            var t = results.CompiledAssembly.GetType("DynamicClass");
            t.GetMethod("Main").Invoke(null, null);
        }
    }
}

Answer 2

Mono has a C# compiler as a service that's usable in .NET applications on Windows (along with Linux, of course).