Expression.Equal Method

Definition

Namespace:

System.Linq.Expressions

Assembly:

System.Linq.Expressions.dll

Creates a BinaryExpression that represents an equality comparison.

Overloads

Equal(Expression, Expression)	Creates a BinaryExpression that represents an equality comparison.
Equal(Expression, Expression, Boolean, MethodInfo)	Creates a BinaryExpression that represents an equality comparison. The implementing method can be specified.

Equal(Expression, Expression)

Source:

BinaryExpression.cs

Creates a BinaryExpression that represents an equality comparison.

public:
 static System::Linq::Expressions::BinaryExpression ^ Equal(System::Linq::Expressions::Expression ^ left, System::Linq::Expressions::Expression ^ right);

public static System.Linq.Expressions.BinaryExpression Equal (System.Linq.Expressions.Expression left, System.Linq.Expressions.Expression right);

static member Equal : System.Linq.Expressions.Expression * System.Linq.Expressions.Expression -> System.Linq.Expressions.BinaryExpression

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

Parameters

left

Expression

An Expression to set the Left property equal to.

right

Expression

An Expression to set the Right property equal to.

Returns

BinaryExpression

A BinaryExpression that has the NodeType property equal to Equal and the Left and Right properties set to the specified values.

Exceptions

ArgumentNullException

left or right is null.

InvalidOperationException

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

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:
// 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.
Console.WriteLine(equalExpr.ToString());

// The following statement first creates an expression tree,
// then compiles it, and then executes it.
Console.WriteLine(
    Expression.Lambda<Func<bool>>(equalExpr).Compile()());

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

' 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.
Console.WriteLine(equalExpr.ToString())

' The following statement first creates an expression tree,
' then compiles it, and then executes it.
Console.WriteLine(
    Expression.Lambda(Of Func(Of Boolean))(equalExpr).Compile()())

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

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 null.

Node Type and Lifted versus Non-Lifted

If the implementing method is not null:

• 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 null:

• 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.

Equal(Expression, Expression, Boolean, MethodInfo)

Source:

BinaryExpression.cs

Creates a BinaryExpression that represents an equality comparison. The implementing method can be specified.

public:
 static System::Linq::Expressions::BinaryExpression ^ Equal(System::Linq::Expressions::Expression ^ left, System::Linq::Expressions::Expression ^ right, bool liftToNull, System::Reflection::MethodInfo ^ method);

public static System.Linq.Expressions.BinaryExpression Equal (System.Linq.Expressions.Expression left, System.Linq.Expressions.Expression right, bool liftToNull, System.Reflection.MethodInfo? method);

static member Equal : System.Linq.Expressions.Expression * System.Linq.Expressions.Expression * bool * System.Reflection.MethodInfo -> System.Linq.Expressions.BinaryExpression

Public Shared Function Equal (left As Expression, right As Expression, liftToNull As Boolean, method As MethodInfo) As BinaryExpression

Parameters

left

Expression

An Expression to set the Left property equal to.

right

Expression

An Expression to set the Right property equal to.

liftToNull

Boolean

true to set IsLiftedToNull to true; false to set IsLiftedToNull to false.

method

MethodInfo

A MethodInfo to set the Method property equal to.

Returns

BinaryExpression

A BinaryExpression that has the NodeType property equal to Equal and the Left, Right, IsLiftedToNull, and Method properties set to the specified values.

Exceptions

ArgumentNullException

left or right is null.

ArgumentException

method is not null and the method it represents returns void, is not static (Shared in Visual Basic), or does not take exactly two arguments.

InvalidOperationException

method is null and 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 and the IsLiftedToNull property is equal to liftToNull. Otherwise, they are both 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 method is not null and it represents a non-void, static (Shared in Visual Basic) method that takes two arguments, it is the implementing method.

• Otherwise, 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 null.

Node Type and Lifted versus Non-Lifted

If the implementing method is not null:

• 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; also, the type of the node is nullable Boolean if liftToNull is true or Boolean if liftToNull is false:

  • 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 null:

• 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 nullable Boolean if liftToNull is true or Boolean if liftToNull is false.