Regex.CompileToAssembly Method (RegexCompilationInfo[], AssemblyName)


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Compiles one or more specified Regex objects to a named assembly.

Namespace:   System.Text.RegularExpressions
Assembly:  System (in System.dll)

[HostProtectionAttribute(SecurityAction.LinkDemand, MayLeakOnAbort = true)]
public static void CompileToAssembly(
	RegexCompilationInfo[] regexinfos,
	AssemblyName assemblyname


Type: System.Text.RegularExpressions.RegexCompilationInfo[]

An array that describes the regular expressions to compile.

Type: System.Reflection.AssemblyName

The file name of the assembly.

Exception Condition

The value of the assemblyname parameter's AssemblyName.Name property is an empty or null string.


The regular expression pattern of one or more objects in regexinfos contains invalid syntax.


assemblyname or regexinfos is null.

The CompileToAssembly(RegexCompilationInfo[], AssemblyName) method generates a .NET Framework assembly in which each regular expression defined in the regexinfos array is represented by a class. Typically, the CompileToAssembly(RegexCompilationInfo[], AssemblyName) method is called from a separate application that generates an assembly of compiled regular expressions. Each regular expression included in the assembly has the following characteristics:

  • It is derived from the Regex class.

  • It is assigned the fully qualified name that is defined by the fullnamespace and name parameters of its corresponding RegexCompilationInfo object.

  • It has a default (or parameterless) constructor.

Ordinarily, the code that instantiates and uses the compiled regular expression is found in an assembly or application that is separate from the code that creates the assembly.

Notes to Callers:

If you are developing on a system that has .NET Framework 4.5 or its point releases installed, you target .NET Framework 4, and you use the CompileToAssembly method to create an assembly that contains compiled regular expressions. Trying to use one of the regular expressions in that assembly on a system that has .NET Framework 4 throws an exception. To work around this problem, you can do either of the following:

  • Build the assembly that contains the compiled regular expressions on a system that has .NET Framework 4 instead of later versions installed.

  • Instead of calling CompileToAssembly and retrieving the compiled regular expression from an assembly, use either static or instance Regex methods with the RegexOptions.Compiled option when you instantiate a Regex object or call a regular expression pattern matching method.

The following example creates an assembly named RegexLib.dll. The assembly includes two compiled regular expressions. The first, Utilities.RegularExpressions.DuplicatedString, matches two identical contiguous words. The second, Utilities.RegularExpressions.EmailAddress, checks whether a string has the correct format to be an e-mail address.

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Text.RegularExpressions;

public class RegexCompilationTest
   public static void Main()
      RegexCompilationInfo expr;
      List<RegexCompilationInfo> compilationList = new List<RegexCompilationInfo>();

      // Define regular expression to detect duplicate words
      expr = new RegexCompilationInfo(@"\b(?<word>\w+)\s+(\k<word>)\b", 
                 RegexOptions.IgnoreCase | RegexOptions.CultureInvariant, 
      // Add info object to list of objects

      // Define regular expression to validate format of email address
      expr = new RegexCompilationInfo(@"^(?("")(""[^""]+?""@)|(([0-9A-Z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9A-Z])@))" + 
                 RegexOptions.IgnoreCase | RegexOptions.CultureInvariant, 
      // Add info object to list of objects

      // Generate assembly with compiled regular expressions
      RegexCompilationInfo[] compilationArray = new RegexCompilationInfo[compilationList.Count];
      AssemblyName assemName = new AssemblyName("RegexLib, Version=, Culture=neutral, PublicKeyToken=null");
      Regex.CompileToAssembly(compilationArray, assemName);                                                 

The regular expression that checks a string for duplicate words is then instantiated and used by the following example.

using System;
using Utilities.RegularExpressions;

public class CompiledRegexUsage
   public static void Main()
      string text = "The the quick brown fox  fox jumped over the lazy dog dog.";
      DuplicatedString duplicateRegex = new DuplicatedString(); 
      if (duplicateRegex.Matches(text).Count > 0)
         Console.WriteLine("There are {0} duplicate words in \n   '{1}'", 
            duplicateRegex.Matches(text).Count, text);
         Console.WriteLine("There are no duplicate words in \n   '{0}'", 
// The example displays the following output to the console:
//    There are 3 duplicate words in
//       'The the quick brown fox  fox jumped over the lazy dog dog.'

Successful compilation of this second example requires a reference to RegexLib.dll (the assembly created by the first example) to be added to the project.

.NET Framework
Available since 1.1
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