Export (0) Print
Expand All

DynamicObject.TryUnaryOperation Method

Provides implementation for unary operations. Classes derived from the DynamicObject class can override this method to specify dynamic behavior for operations such as negation, increment, or decrement.

Namespace:  System.Dynamic
Assembly:  System.Core (in System.Core.dll)

public virtual bool TryUnaryOperation(
	UnaryOperationBinder binder,
	out Object result
)

Parameters

binder
Type: System.Dynamic.UnaryOperationBinder

Provides information about the unary operation. The binder.Operation property returns an ExpressionType object. For example, for the negativeNumber = -number statement, where number is derived from the DynamicObject class, binder.Operation returns "Negate".

result
Type: System.Object

The result of the unary operation.

Return Value

Type: System.Boolean
true if the operation is successful; otherwise, false. If this method returns false, the run-time binder of the language determines the behavior. (In most cases, a language-specific run-time exception is thrown.)

Classes derived from the DynamicObject class can override this method to specify how unary operations should be performed for a dynamic object. When the method is not overridden, the run-time binder of the language determines the behavior. (In most cases, a language-specific run-time exception is thrown.)

This method is called when you have unary operations such as negation, increment, or decrement. For example, if the TryUnaryOperation method is overridden, this method is automatically invoked for statements like negativeNumber = -number, where number is derived from the DynamicObject class.

You can get information about the type of the unary operation by using the Operation property of the binder parameter.

If your dynamic object is used only in C# and Visual Basic, the binder.Operation property can have one of the following values from the ExpressionType enumeration. However, in other languages such as IronPython or IronRuby, you can have other values. For more information about ExpressionType, see documentation on the CodePlex Web site.

Value

Description

C#

Visual Basic

Decrement

A unary decrement operation.

a--

Not supported.

Increment

A unary increment operation.

a++

Not supported.

Negate

An arithmetic negation.

-a

-a

Not

A logical negation.

!a

Not a

OnesComplement

A ones complement.

~a

Not supported.

IsFalse

A false condition value.

a && b

Not supported.

IsTrue

A true condition value.

a || b

Not supported.

UnaryPlus

A unary plus.

+a

+a

NoteNote

To implement OrElse (a || b) and AndAlso (a && b) operations for dynamic objects in C#, you may want to implement both the TryUnaryOperation method and the TryBinaryOperation method.

The OrElse operation consists of the unary IsTrue operation and the binary Or operation. The Or operation is performed only if the result of the IsTrue operation is false.

The AndAlso operation consists of the unary IsFalse operation and the binary And operation. The And operation is performed only if the result of the IsFalse operation is false.

Assume that you need a data structure to store textual and numeric representations of numbers, and you want to define a mathematical negation operation for such data.

The following code example demonstrates the DynamicNumber class, which is derived from the DynamicObject class. DynamicNumber overrides the TryUnaryOperation method to enable the mathematical negation operation. Is also overrides the TrySetMember and TryGetMember methods to enable access to the elements.

In this example, only the mathematical negation operation is supported. If you try to write a statement like negativeNumber = +number, a run-time exception occurs.

// Add using System.Linq.Expressions; 
// to the beginning of the file 

// The class derived from DynamicObject. 
public class DynamicNumber : DynamicObject
{
    // The inner dictionary to store field names and values.
    Dictionary<string, object> dictionary
        = new Dictionary<string, object>();

    // Get the property value. 
    public override bool TryGetMember(
        GetMemberBinder binder, out object result)
    {
        return dictionary.TryGetValue(binder.Name, out result);
    }

    // Set the property value. 
    public override bool TrySetMember(
        SetMemberBinder binder, object value)
    {
        dictionary[binder.Name] = value;
        return true;
    }

    // Perform the unary operation.  
    public override bool TryUnaryOperation(
        UnaryOperationBinder binder, out object result)
    {
        // The Textual property contains  
        // the name of the unary operation in addition  
        // to the textual representaion of the number. 
        string resultTextual =
             binder.Operation + " " +
             dictionary["Textual"].ToString();
        int resultNumeric;

        // Determining what type of operation is being performed. 
        switch (binder.Operation)
        {
            case ExpressionType.Negate:
                resultNumeric =
                     -(int)dictionary["Numeric"];
                break;
            default:
                // In case of any other unary operation, 
                // print out the type of operation and return false, 
                // which means that the language should determine  
                // what to do. 
                // (Usually the language just throws an exception.)            
                Console.WriteLine(
                    binder.Operation +
                    ": This unary operation is not implemented");
                result = null;
                return false;
        }

        dynamic finalResult = new DynamicNumber();
        finalResult.Textual = resultTextual;
        finalResult.Numeric = resultNumeric;
        result = finalResult;
        return true;
    }
}

class Program
{
    static void Test(string[] args)
    {
        // Creating the first dynamic number.
        dynamic number = new DynamicNumber();

        // Creating properties and setting their values 
        // for the dynamic number. 
        // The TrySetMember method is called.
        number.Textual = "One";
        number.Numeric = 1;

        // Printing out properties. The TryGetMember method is called.
        Console.WriteLine(
            number.Textual + " " + number.Numeric);

        dynamic negativeNumber = new DynamicNumber();

        // Performing a mathematical negation. 
        // TryUnaryOperation is called.
        negativeNumber = -number;

        Console.WriteLine(
            negativeNumber.Textual + " " + negativeNumber.Numeric);

        // The following statement produces a run-time exception 
        // because the unary plus operation is not implemented. 
        // negativeNumber = +number;
    }
}

// This code example produces the following output: 

// One 1 
// Negate One -1

.NET Framework

Supported in: 4.5, 4

.NET Framework Client Profile

Supported in: 4

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

Show:
© 2014 Microsoft