Roslyn compile source without writing to disk on the same AppDomain.

gistfile1.cs

using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;

namespace RoslynNuget
{

    public interface IRunnableFromLoadedAssembly
    {
        void Run();
    }

    public class LoadAssemblyProgram
    {        
        static void Main(string[] args)
        {
            var assembly = Compile(@"
using System;
using System.IO;
using RoslynNuget;

public class MyType : IRunnableFromLoadedAssembly
{
    public void Run ()
    {
        Console.WriteLine (""It's alive."");
    }
}
");
            var type = assembly.GetType("MyType");
            var obj = (IRunnableFromLoadedAssembly) Activator.CreateInstance(type);
            obj.Run();

            Console.ReadLine();
        }

        public static Assembly Compile(params string[] sources)
        {
            var assemblyFileName = "gen" + Guid.NewGuid().ToString().Replace("-", "") + ".dll";
            var compilation = CSharpCompilation.Create(assemblyFileName,
                options: new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary),
                syntaxTrees: from source in sources
                             select CSharpSyntaxTree.ParseText(source),
                references: new[]
                {
                    new MetadataFileReference(typeof(object).Assembly.Location),
                    new MetadataFileReference(typeof(RuntimeBinderException).Assembly.Location),
                    new MetadataFileReference(typeof(DynamicAttribute).Assembly.Location),
                    new MetadataFileReference(typeof(LoadAssemblyProgram).Assembly.Location)
                });

            EmitResult emitResult;

            using (var ms = new MemoryStream())
            {
                emitResult = compilation.Emit(ms);
                if (emitResult.Success)
                {
                    var assembly = Assembly.Load(ms.GetBuffer());
                    return assembly;
                }
            }

            var message = string.Join("\r\n", emitResult.Diagnostics);
            throw new Exception(message);
        }
    }
}