Runtime C# Expression Evaluator

This is a simple class library (or just .cs file if you wish) to allow for runtime compilation and evaluation of C# code blocks. There are both static methods of the Evaluator class that allow for simple use (but at a performance penalty) or you can use the object directly to create multiple evaluations:

 

Console.WriteLine("Test0: {0}", Evaluator.EvaluateToInteger("(30 + 4) * 2")); Console.WriteLine("Test1: {0}", Evaluator.EvaluateToString("/"Hello /" + /"There/"")); Console.WriteLine("Test2: {0}", Evaluator.EvaluateToBool("30 == 40")); Console.WriteLine("Test3: {0}", Evaluator.EvaluateToObject("new DataSet()")); EvaluatorItem[] items = { new EvaluatorItem(typeof(int), "(30 + 4) * 2", "GetNumber"), new EvaluatorItem(typeof(string), "/"Hello /" + /"There/"", "GetString"), new EvaluatorItem(typeof(bool), "30 == 40", "GetBool"), new EvaluatorItem(typeof(object), "new DataSet()", "GetDataSet") }; Evaluator eval = new Evaluator(items); Console.WriteLine("TestStatic0: {0}", eval.EvaluateInt("GetNumber")); Console.WriteLine("TestStatic1: {0}", eval.EvaluateString("GetString")); Console.WriteLine("TestStatic2: {0}", eval.EvaluateBool("GetBool")); Console.WriteLine("TestStatic3: {0}", eval.Evaluate("GetDataSet"));

 

How does it work? I am using the CodeDOM to create a simple assembly with a single class in it. I simply transform each of the EvaluatorItem s into a method of the class. When you call EvaluateInt() or Evaluate() , I use reflection to get a MethodInfo object and call the method.

The source code comes packaged in a Class Library with a Test program that you can use to get examples of use:

To compile the expressions, I am creating a new CSharpCodeProvider and setting Compiler attributes (like adding references, telling it to generate it in memory, etc.). Then I am building a dummy class that I can append my methods on. Lastly I compile it (check for errors) and save the object to use to call with the MethodInfo structure:

 

ICodeCompiler comp = (new CSharpCodeProvider().CreateCompiler()); CompilerParameters cp = new CompilerParameters(); cp.ReferencedAssemblies.Add("system.dll"); cp.ReferencedAssemblies.Add("system.data.dll"); cp.ReferencedAssemblies.Add("system.xml.dll"); cp.GenerateExecutable = false; cp.GenerateInMemory = true; StringBuilder code = new StringBuilder(); code.Append("using System; /n"); code.Append("using System.Data; /n"); code.Append("using System.Data.SqlClient; /n"); code.Append("using System.Data.OleDb; /n"); code.Append("using System.Xml; /n"); code.Append("namespace ADOGuy { /n"); code.Append(" public class _Evaluator { /n"); foreach(EvaluatorItem item in items) { code.AppendFormat(" public {0} {1}() ", item.ReturnType.Name, item.Name); code.Append("{ "); code.AppendFormat(" return ({0}); ", item.Expression); code.Append("}/n"); } code.Append("} }"); CompilerResults cr = comp.CompileAssemblyFromSource(cp, code.ToString()); if (cr.Errors.HasErrors) { StringBuilder error = new StringBuilder(); error.Append("Error Compiling Expression: "); foreach (CompilerError err in cr.Errors) { error.AppendFormat("{0}/n", err.ErrorText); } throw new Exception("Error Compiling Expression: " + error.ToString()); } Assembly a = cr.CompiledAssembly; _Compiled = a.CreateInstance("ADOGuy._Evaluator");

 

When I call the _Compiled object, I use a MethodInfo object to Invoke the call and return the result to the user:

 

public object Evaluate(string name) { MethodInfo mi = _Compiled.GetType().GetMethod(name); return mi.Invoke(_Compiled, null); }

 

（轉自：http://www.codeproject.com/KB/cs/runtime_eval.aspx）