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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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Introduction

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 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.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);
}
    

License

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

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About the Author

Shawn Wildermuth

United States United States
No Biography provided

Comments and Discussions

 
GeneralMy vote of 5 PinmemberIgor Gresovnik16-Aug-10 11:58 
GeneralThanks Pinmemberjigi_chavan13-Oct-09 1:02 
Generalpls help PinmemberXandip30-Sep-09 4:50 
Generalgreat tool! Pinmemberabomb2229-May-09 5:10 
RantDownload link is not working Pinmemberparslej27-Mar-09 4:58 
GeneralBoolean expression evaluator Pinmemberjackietrillo17-Feb-09 17:22 
AnswerRe: Boolean expression evaluator PinmemberMember 378665520-Feb-09 10:37 
QuestionLicence ? Pinmemberasalmi16-Sep-08 6:12 
AnswerRe: Licence ? Pinmembergonzalito_uy11-Feb-10 6:19 
Questiondoes it evaluate the expression ? PinmemberParesh Gheewala7-Aug-08 21:21 
GeneralGarbage Collection PinmemberTGKelley14-Aug-07 15:25 
Questioncan a web project use "ReferencedAssemblies.Add("customer.dll")" Pinmemberwlbkeats7-Dec-06 23:34 
GeneralEval custom classes PinmemberPluisjeh15-Mar-06 0:41 
GeneralEval Objects PinmemberZiggY816-Mar-06 3:52 
GeneralIt's Great! PinmemberJames Yang20-Feb-06 3:16 
GeneralGreat Article Pinmemberguruji3239-Nov-04 15:32 
GeneralPerformance penalty Pinmemberjelo_118-Jan-03 22:30 
Generalpassing arguments PinsussZiv Rosenzweig24-Jul-02 5:26 
GeneralC# Parser Generator Pinmemberjhreich22-Jul-02 3:48 
GeneralRe: C# Parser Generator PinsussAnonymous23-Jul-02 17:33 
GeneralRe: C# Parser Generator PinmemberJeff Varszegi25-Apr-04 20:29 
GeneralRe: C# Parser Generator PinmemberKeith Rule11-Nov-05 6:35 
GeneralI like to know more... how to put the assembly into a SQL2000 Binary field... PinmemberChris Muench19-Jun-02 17:50 
GeneralTotally amazing PinmemberNielsH24-May-02 9:29 
GeneralGreat! PinmemberHolger Persch22-Apr-02 20:02 

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