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CodeDefaultValueExpression Class

Represents a reference to a default value.

Namespace:  System.CodeDom
Assembly:  System (in System.dll)

[SerializableAttribute]
[ComVisibleAttribute(true)]
[ClassInterfaceAttribute(ClassInterfaceType.AutoDispatch)]
public class CodeDefaultValueExpression : CodeExpression

A CodeDefaultValueExpression can be used to represent a reference to a default value.

The Type property specifies the reference to the value type. The CodeDefaultValueExpression class is used in the generation of generics-based code. For more information on generics, see Generics in the .NET Framework Class Library (C# Programming Guide). The following code steps are provided in this section to further describe the use of the CodeDefaultValueExpression class to add a new default value to a code graph.

The code in part 1 is part of a larger example provided for the CodeTypeParameter class. This code, when run through the C# code generator, results in the C# code that appears in part 2. When this code is called in the statement in part 3, the result is the output shown in part 4.

// Part 1: Code to create a generic Print method.
            CodeMemberMethod printMethod = new CodeMemberMethod();
            CodeTypeParameter sType = new CodeTypeParameter("S");
            sType.HasConstructorConstraint = true;
            CodeTypeParameter tType = new CodeTypeParameter("T");
            sType.HasConstructorConstraint = true;

            printMethod.Name = "Print";
            printMethod.TypeParameters.Add(sType);
            printMethod.TypeParameters.Add(tType);
            printMethod.Statements.Add(ConsoleWriteLineStatement(
                new CodeDefaultValueExpression(new CodeTypeReference("T"))));
            printMethod.Statements.Add(ConsoleWriteLineStatement(
                new CodeDefaultValueExpression(new CodeTypeReference("S"))));

// Part 2: Code generated by code in part 1.
public virtual void Print<S, T>()
            where S : new()
         {
            Console.WriteLine(default(T));
            Console.WriteLine(default(S));
        }

// Part 3: Call to the generated method.
dict.Print<System.Decimal, int>();

// Part 4: Output of the generated method.
0
0

The following code example shows the use of the CodeDefaultValueExpression to create default values for decimal and integer parameters. This example is part of a larger example provided for the CodeTypeParameter class.

printMethod.Statements.Add(ConsoleWriteLineStatement(
    new CodeDefaultValueExpression(new CodeTypeReference("T"))));
printMethod.Statements.Add(ConsoleWriteLineStatement(
    new CodeDefaultValueExpression(new CodeTypeReference("S"))));

System.Object
  System.CodeDom.CodeObject
    System.CodeDom.CodeExpression
      System.CodeDom.CodeDefaultValueExpression

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0

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