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Expression.Equal Method (Expression, Expression)

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Creates a BinaryExpression that represents an equality comparison.

Namespace:  System.Linq.Expressions
Assembly:  System.Core (in System.Core.dll)

Syntax

'Declaration
Public Shared Function Equal ( _
    left As Expression, _
    right As Expression _
) As BinaryExpression

public static BinaryExpression Equal(
    Expression left,
    Expression right
)

Parameters

Return Value

Type: System.Linq.Expressions.BinaryExpression
A BinaryExpression that has the NodeType property equal to Equal and the Left and Right properties set to the specified values.

Exceptions

Exception Condition
ArgumentNullException

left or right is nulla null reference (Nothing in Visual Basic).
InvalidOperationException

The equality operator is not defined for left.Type and right.Type.

Remarks

The resulting BinaryExpression has the Method property set to the implementing method. The Type property is set to the type of the node. If the node is lifted, the IsLifted property is true. Otherwise, it is false. The IsLiftedToNull property is always false. The following information describes the implementing method, the node type, and whether a node is lifted.

Implementing Method

The following rules determine the implementing method for the operation:

  • If the Type property of either left or right represents a user-defined type that overloads the equality operator, the MethodInfo that represents that method is the implementing method.

  • Otherwise, the implementing method is nulla null reference (Nothing in Visual Basic).

Node Type and Lifted versus Non-Lifted

If the implementing method is not nulla null reference (Nothing in Visual Basic):

  • If left.Type and right.Type are assignable to the corresponding argument types of the implementing method, the node is not lifted. The type of the node is the return type of the implementing method.

  • If the following two conditions are satisfied, the node is lifted and the type of the node is Boolean:

    • left.Type and right.Type are both value types of which at least one is nullable and the corresponding non-nullable types are equal to the corresponding argument types of the implementing method.

    • The return type of the implementing method is Boolean.

If the implementing method is nulla null reference (Nothing in Visual Basic):

  • If left.Type and right.Type are both non-nullable, the node is not lifted. The type of the node is Boolean.

  • If left.Type and right.Type are both nullable, the node is lifted. The type of the node is Boolean.

Examples

The following code example shows how to create an expression that checks whether the values of its two arguments are equal.

' Add the following directive to your file:
' Imports System.Linq.Expressions  

' This expression compares the values of its two arguments.
' Both arguments must be of the same type.
Dim equalExpr As Expression = Expression.Equal(
    Expression.Constant(42),
    Expression.Constant(45)
)

' Print the expression.
outputBlock.Text &= equalExpr.ToString() & vbCrLf

' The following statement first creates an expression tree,
' then compiles it, and then executes it.
outputBlock.Text &=
    Expression.Lambda(Of Func(Of Boolean))(equalExpr).Compile()() & vbCrLf

' This code example produces the following output:
'
' (42 == 45)
' False

// Add the following directive to your file:
// using System.Linq.Expressions;  

// This expression compares the values of its two arguments.
// Both arguments need to be of the same type.
Expression equalExpr = Expression.Equal(
    Expression.Constant(42),
    Expression.Constant(45)
);

// Print out the expression.
outputBlock.Text += equalExpr.ToString() + "\n";

// The following statement first creates an expression tree,
// then compiles it, and then executes it.
outputBlock.Text +=
    Expression.Lambda<Func<bool>>(equalExpr).Compile()() + "\n";

// This code example produces the following output:
//
// (42 == 45)
// False

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.