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Posted 20 Apr 2002

Runtime C# Expression Evaluator

, 20 Apr 2002
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A C# class (and library if needed) to do runtime evaluations of C# expressions
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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\"", 
                          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 EvaluatorItems 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.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}() ", 
  code.Append("{ ");
  code.AppendFormat("      return ({0}); ", item.Expression);
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);


This article, along with any associated source code and files, is licensed under The Microsoft Public License (Ms-PL)


About the Author

Shawn Wildermuth
United States United States
No Biography provided

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Comments and Discussions

GeneralMy vote of 5 Pin
Renju Vinod9-May-13 2:14
professionalRenju Vinod9-May-13 2:14 
QuestionString Expression evaluation Pin
specialdreamsin13-Jun-12 23:27
memberspecialdreamsin13-Jun-12 23:27 
QuestionUsage of this code Pin
gonzalito_uy24-Apr-12 17:14
membergonzalito_uy24-Apr-12 17:14 
QuestionWhat about Double type ? Pin
Kronborn28-Mar-12 2:16
memberKronborn28-Mar-12 2:16 
GeneralMy vote of 5 Pin
MohammadAmiry3-Nov-11 1:30
memberMohammadAmiry3-Nov-11 1:30 
Excellent; thank you.
I just get the following obsolescence warning in .net 4:

<br />
<br />
Warning	1	'System.CodeDom.Compiler.CodeDomProvider.CreateCompiler()' is obsolete: 'Callers should not use the ICodeCompiler interface and should instead use the methods directly on the CodeDomProvider class. Those inheriting from CodeDomProvider must still implement this interface, and should exclude this warning or also obsolete this method.'	E:\My Projects\Evaluator\Evaluator.cs	35	29	Evaluator<br />

GeneralMy vote of 5 Pin
Nagy Vilmos2-May-11 0:18
memberNagy Vilmos2-May-11 0:18 
GeneralMy vote of 5 Pin
Yvan Rodrigues28-Mar-11 10:47
memberYvan Rodrigues28-Mar-11 10:47 
GeneralMy vote of 5 Pin
joyichantg21-Mar-11 20:30
memberjoyichantg21-Mar-11 20:30 
GeneralMy vote of 5 Pin
kaikg31-Aug-10 4:51
memberkaikg31-Aug-10 4:51 
GeneralGood job! Pin
kaikg31-Aug-10 4:51
memberkaikg31-Aug-10 4:51 
GeneralMy vote of 5 Pin
Igor Gresovnik16-Aug-10 11:58
memberIgor Gresovnik16-Aug-10 11:58 
GeneralThanks Pin
jigi_chavan13-Oct-09 1:02
memberjigi_chavan13-Oct-09 1:02 
Generalpls help Pin
Xandip30-Sep-09 4:50
memberXandip30-Sep-09 4:50 
Generalgreat tool! Pin
abomb2229-May-09 5:10
memberabomb2229-May-09 5:10 
RantDownload link is not working Pin
parslej27-Mar-09 4:58
memberparslej27-Mar-09 4:58 
GeneralBoolean expression evaluator Pin
jackietrillo17-Feb-09 17:22
memberjackietrillo17-Feb-09 17:22 
AnswerRe: Boolean expression evaluator Pin
Member 378665520-Feb-09 10:37
memberMember 378665520-Feb-09 10:37 
QuestionLicence ? Pin
asalmi16-Sep-08 6:12
memberasalmi16-Sep-08 6:12 
AnswerRe: Licence ? Pin
gonzalito_uy11-Feb-10 6:19
membergonzalito_uy11-Feb-10 6:19 
Questiondoes it evaluate the expression ? Pin
Paresh Gheewala7-Aug-08 21:21
memberParesh Gheewala7-Aug-08 21:21 
GeneralGarbage Collection Pin
TGKelley14-Aug-07 15:25
memberTGKelley14-Aug-07 15:25 
Questioncan a web project use "ReferencedAssemblies.Add("customer.dll")" Pin
wlbkeats7-Dec-06 23:34
memberwlbkeats7-Dec-06 23:34 
GeneralEval custom classes Pin
Pluisjeh15-Mar-06 0:41
memberPluisjeh15-Mar-06 0:41 
GeneralEval Objects Pin
ZiggY816-Mar-06 3:52
memberZiggY816-Mar-06 3:52 
GeneralIt's Great! Pin
James Yang20-Feb-06 3:16
memberJames Yang20-Feb-06 3:16 
GeneralGreat Article Pin
guruji3239-Nov-04 15:32
memberguruji3239-Nov-04 15:32 
GeneralPerformance penalty Pin
jelo_118-Jan-03 22:30
memberjelo_118-Jan-03 22:30 
Generalpassing arguments Pin
Ziv Rosenzweig24-Jul-02 5:26
sussZiv Rosenzweig24-Jul-02 5:26 
GeneralC# Parser Generator Pin
jhreich22-Jul-02 3:48
memberjhreich22-Jul-02 3:48 
GeneralRe: C# Parser Generator Pin
Anonymous23-Jul-02 17:33
sussAnonymous23-Jul-02 17:33 
GeneralRe: C# Parser Generator Pin
Jeff Varszegi25-Apr-04 20:29
memberJeff Varszegi25-Apr-04 20:29 
GeneralRe: C# Parser Generator Pin
Keith Rule11-Nov-05 6:35
memberKeith Rule11-Nov-05 6:35 
GeneralI like to know more... how to put the assembly into a SQL2000 Binary field... Pin
Chris Muench19-Jun-02 17:50
memberChris Muench19-Jun-02 17:50 
GeneralTotally amazing Pin
NielsH24-May-02 9:29
memberNielsH24-May-02 9:29 
GeneralGreat! Pin
Holger Persch22-Apr-02 20:02
memberHolger Persch22-Apr-02 20:02 
Generalseriously cool! Pin
ector22-Apr-02 4:56
memberector22-Apr-02 4:56 

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