DynamicObject.TryBinaryOperation Method

Definition

Namespace:

System.Dynamic

Assembly:

System.Linq.Expressions.dll

Source:

DynamicObject.cs

Provides implementation for binary operations. Classes derived from the DynamicObject class can override this method to specify dynamic behavior for operations such as addition and multiplication.

public:
 virtual bool TryBinaryOperation(System::Dynamic::BinaryOperationBinder ^ binder, System::Object ^ arg, [Runtime::InteropServices::Out] System::Object ^ % result);

public virtual bool TryBinaryOperation (System.Dynamic.BinaryOperationBinder binder, object arg, out object? result);

abstract member TryBinaryOperation : System.Dynamic.BinaryOperationBinder * obj * obj -> bool
override this.TryBinaryOperation : System.Dynamic.BinaryOperationBinder * obj * obj -> bool

Public Overridable Function TryBinaryOperation (binder As BinaryOperationBinder, arg As Object, ByRef result As Object) As Boolean

Parameters

binder

BinaryOperationBinder

Provides information about the binary operation. The binder.Operation property returns an ExpressionType object. For example, for the sum = first + second statement, where first and second are derived from the DynamicObject class, binder.Operation returns ExpressionType.Add.

arg

Object

The right operand for the binary operation. For example, for the sum = first + second statement, where first and second are derived from the DynamicObject class, arg is equal to second.

result

Object

The result of the binary operation.

Returns

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.)

Examples

Assume that you need a data structure to store textual and numeric representations of numbers, and you want to define basic mathematical operations such as addition and subtraction for such data.

The following code example demonstrates the DynamicNumber class, which is derived from the DynamicObject class. DynamicNumber overrides the TryBinaryOperation method to enable mathematical operations. It also overrides the TrySetMember and TryGetMember methods to enable access to the elements.

In this example, only addition and subtraction operations are supported. If you try to write a statement like resultNumber = firstNumber*secondNumber, a run-time exception is thrown.

// 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 binary operation.
    public override bool TryBinaryOperation(
        BinaryOperationBinder binder, object arg, out object result)
    {
        // The Textual property contains the textual representaion
        // of two numbers, in addition to the name
        // of the binary operation.
        string resultTextual =
            dictionary["Textual"].ToString() + " "
            + binder.Operation + " " +
            ((DynamicNumber)arg).dictionary["Textual"].ToString();

        int resultNumeric;

        // Checking what type of operation is being performed.
        switch (binder.Operation)
        {
            // Proccessing mathematical addition (a + b).
            case ExpressionType.Add:
                resultNumeric =
                    (int)dictionary["Numeric"] +
                    (int)((DynamicNumber)arg).dictionary["Numeric"];
                break;

            // Processing mathematical substraction (a - b).
            case ExpressionType.Subtract:
                resultNumeric =
                    (int)dictionary["Numeric"] -
                    (int)((DynamicNumber)arg).dictionary["Numeric"];
                break;

            // In case of any other binary 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.)
            default:
                Console.WriteLine(
                    binder.Operation +
                    ": This binary 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 firstNumber = new DynamicNumber();

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

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

        // Creating the second dynamic number.
        dynamic secondNumber = new DynamicNumber();
        secondNumber.Textual = "Two";
        secondNumber.Numeric = 2;
        Console.WriteLine(
            secondNumber.Textual + " " + secondNumber.Numeric);

        dynamic resultNumber = new DynamicNumber();

        // Adding two numbers. The TryBinaryOperation is called.
        resultNumber = firstNumber + secondNumber;

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

        // Subtracting two numbers. TryBinaryOperation is called.
        resultNumber = firstNumber - secondNumber;

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

        // The following statement produces a run-time exception
        // because the multiplication operation is not implemented.
        // resultNumber = firstNumber * secondNumber;
    }
}

// This code example produces the following output:

// One 1
// Two 2
// One Add Two 3
// One Subtract Two -1

' Add Imports System.Linq.Expressions
' to the beginning of the file.
' The class derived from DynamicObject.
Public Class DynamicNumber
    Inherits DynamicObject

    ' The inner dictionary to store field names and values.
    Dim dictionary As New Dictionary(Of String, Object)

    ' Get the property value.
    Public Overrides Function TryGetMember(
        ByVal binder As System.Dynamic.GetMemberBinder,
        ByRef result As Object) As Boolean

        Return dictionary.TryGetValue(binder.Name, result)

    End Function

    ' Set the property value.
    Public Overrides Function TrySetMember(
        ByVal binder As System.Dynamic.SetMemberBinder,
        ByVal value As Object) As Boolean

        dictionary(binder.Name) = value
        Return True

    End Function

    ' Perform the binary operation. 
    Public Overrides Function TryBinaryOperation(
        ByVal binder As System.Dynamic.BinaryOperationBinder,
        ByVal arg As Object, ByRef result As Object) As Boolean

        ' The Textual property contains the textual representaion 
        ' of two numbers, in addition to the name of the binary operation.
        Dim resultTextual As String =
            dictionary("Textual") & " " &
            binder.Operation.ToString() & " " &
        CType(arg, DynamicNumber).dictionary("Textual")

        Dim resultNumeric As Integer

        ' Checking what type of operation is being performed.
        Select Case binder.Operation
            ' Proccessing mathematical addition (a + b).
            Case ExpressionType.Add
                resultNumeric =
                CInt(dictionary("Numeric")) +
                CInt((CType(arg, DynamicNumber)).dictionary("Numeric"))

                ' Processing mathematical substraction (a - b).
            Case ExpressionType.Subtract
                resultNumeric =
                CInt(dictionary("Numeric")) -
                CInt((CType(arg, DynamicNumber)).dictionary("Numeric"))

            Case Else
                ' In case of any other binary 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.ToString() &
                    ": This binary operation is not implemented")
                result = Nothing
                Return False
        End Select

        Dim finalResult As Object = New DynamicNumber()
        finalResult.Textual = resultTextual
        finalResult.Numeric = resultNumeric
        result = finalResult
        Return True
    End Function
End Class

Sub Test()
    ' Creating the first dynamic number.
    Dim firstNumber As Object = New DynamicNumber()

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

    ' Printing out properties. The TryGetMember method is called.
    Console.WriteLine(
        firstNumber.Textual & " " & firstNumber.Numeric)

    ' Creating the second dynamic number.
    Dim secondNumber As Object = New DynamicNumber()
    secondNumber.Textual = "Two"
    secondNumber.Numeric = 2
    Console.WriteLine(
        secondNumber.Textual & " " & secondNumber.Numeric)

    Dim resultNumber As Object = New DynamicNumber()

    ' Adding two numbers. TryBinaryOperation is called.
    resultNumber = firstNumber + secondNumber
    Console.WriteLine(
        resultNumber.Textual & " " & resultNumber.Numeric)

    ' Subtracting two numbers. TryBinaryOperation is called.
    resultNumber = firstNumber - secondNumber
    Console.WriteLine(
        resultNumber.Textual & " " & resultNumber.Numeric)

    ' The following statement produces a run-time exception
    ' because the multiplication operation is not implemented.
    ' resultNumber = firstNumber * secondNumber
End Sub

' This code example produces the following output:

' One 1
' Two 2
' One Add Two 3
' One Subtract Two -1

Remarks

Classes derived from the DynamicObject class can override this method to specify how binary 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 binary operations such as addition or multiplication. For example, if the TryBinaryOperation method is overridden, it is automatically invoked for statements like sum = first + second or multiply = first*second, where first is derived from the DynamicObject class.

You can get information about the type of the binary 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.

Value	Description	C#	Visual Basic
Add	An addition operation without overflow checking, for numeric operands.	a + b	a + b
AddAssign	An addition compound assignment operation without overflow checking, for numeric operands.	a += b	Not supported.
And	A bitwise AND operation.	a & b	a And b
AndAssign	A bitwise AND compound assignment operation.	a &= b	Not supported.
Divide	An arithmetic division operation.	a / b	a / b
DivideAssign	An arithmetic division compound assignment operation.	a /= b	Not supported.
ExclusiveOr	A bitwise XOR operation.	a ^ b	a Xor b
ExclusiveOrAssign	A bitwise XOR compound assignment operation.	a ^= b	Not supported.
GreaterThan	A "greater than" comparison.	a > b	a > b
GreaterThanOrEqual	A "greater than or equal to" comparison.	a >= b	Not supported.
LeftShift	A bitwise left-shift operation.	a << b	a << b
LeftShiftAssign	A bitwise left-shift compound assignment operation.	a <<= b	Not supported.
LessThan	A "less than" comparison.	a < b	a < b
LessThanOrEqual	A "less than or equal to" comparison.	a <= b	Not supported.
Modulo	An arithmetic remainder operation.	a % b	a Mod b
ModuloAssign	An arithmetic remainder compound assignment operation.	a %= b	Not supported.
Multiply	A multiplication operation without overflow checking, for numeric operands.	a * b	a * b
MultiplyAssign	A multiplication compound assignment operation without overflow checking, for numeric operands.	a *= b	Not supported.
NotEqual	An inequality comparison.	a != b	a <> b
Or	A bitwise or logical OR operation.	a &#124; b	a Or b
OrAssign	A bitwise or logical OR compound assignment.	a &#124;= b	Not supported.
Power	A mathematical operation of raising a number to a power.	Not supported.	a ^ b
RightShift	A bitwise right-shift operation.	a >> b	a >> b
RightShiftAssign	A bitwise right-shift compound assignment operation.	a >>= b	Not supported.
Subtract	A subtraction operation without overflow checking, for numeric operands.	a - b	a - b
SubtractAssign	A subtraction compound assignment operation without overflow checking, for numeric operands.	a -= b	Not supported.

Note

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.