Article
11/18/2011

IndexExpression Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Represents indexing a property or array.

Inheritance Hierarchy

System.Object
System.Linq.Expressions.Expression
System.Linq.Expressions.IndexExpression

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

Syntax

'Declaration
Public NotInheritable Class IndexExpression _
    Inherits Expression

public sealed class IndexExpression : Expression

The IndexExpression type exposes the following members.

Properties

	Name	Description
	Arguments	Gets the arguments that will be used to index the property or array.
	CanReduce	Indicates that the node can be reduced to a simpler node. If this returns true, Reduce() can be called to produce the reduced form. (Inherited from Expression.)
	Indexer	Gets the PropertyInfo for the property if the expression represents an indexed property, returns null otherwise.
	NodeType	Returns the node type of this Expression. (Overrides Expression.NodeType.)
	Object	An object to index.
	Type	Gets the static type of the expression that this Expression represents. (Overrides Expression.Type.)

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Methods

	Name	Description
	Accept	Dispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall. (Inherited from Expression.)
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	Reduce	Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression.)
	ReduceAndCheck	Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression.)
	ReduceExtensions	Reduces the expression to a known node type (that is not an Extension node) or just returns the expression if it is already a known type. (Inherited from Expression.)
	ToString	Returns a textual representation of the Expression. (Inherited from Expression.)
	Update	Creates a new expression that is like this one, but using the supplied children. If all of the children are the same, it will return this expression.
	VisitChildren	Reduces the node and then calls the visitor delegate on the reduced expression. The method throws an exception if the node is not reducible. (Inherited from Expression.)

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Examples

The following code example shows how to create an object of the IndexExpression type and use it to change a value of an array element by using the ArrayAccess method.

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

' This parameter expression represents a variable that will hold the array.
Dim arrayExpr As ParameterExpression = Expression.Parameter(GetType(Integer()), "Array")

' This parameter expression represents an array index.
' For multidimensional arrays, you can define several indexes. 
Dim indexExpr As ParameterExpression = Expression.Parameter(GetType(Integer), "Index")

' This parameter represents the value that will be added to a corresponding array element.
Dim valueExpr As ParameterExpression = Expression.Parameter(GetType(Integer), "Value")

' This expression represents an array access operation.
' It can be used for assigning to, or reading from, an array element.
Dim arrayAccessExpr As Expression = Expression.ArrayAccess(
    arrayExpr,
    indexExpr
)

' This lambda expression assigns a value provided to it to a specified array element.
' The array, the index of the array element, and the value to be added to the element
' are parameters of the lambda expression.
Dim lambdaExpr As Expression(Of Func(Of Integer(), Integer, Integer, Integer)) = 
    Expression.Lambda(Of Func(Of Integer(), Integer, Integer, Integer))( 
        Expression.Assign(arrayAccessExpr, Expression.Add(arrayAccessExpr, valueExpr)), 
    arrayExpr,
    indexExpr, 
    valueExpr 
  )

' Print expressions.
outputBlock.Text &= "Array Access Expression:" & vbCrLf
outputBlock.Text &= arrayAccessExpr.ToString() & vbCrLf

outputBlock.Text &= "Lambda Expression:" & vbCrLf
outputBlock.Text &= lambdaExpr.ToString() & vbCrLf

outputBlock.Text &= "The result of executing the lambda expression:" & vbCrLf

' The following statement first creates an expression tree,
' then compiles it, and then executes it.
' Parameters passed to the Invoke method are passed to the lambda expression.
outputBlock.Text &= lambdaExpr.Compile().Invoke(New Integer() {10, 20, 30}, 0, 5) & vbCrLf

' This code example produces the following output:
'
' Array Access Expression:
' Array[Index]

' Lambda Expression:
' (Array, Index, Value) => (Array[Index] = (Array[Index] + Value))

' The result of executing the lambda expression:
' 15

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

       // This parameter expression represents a variable that will hold the array.
       ParameterExpression arrayExpr = Expression.Parameter(typeof(int[]), "Array");

       // This parameter expression represents an array index.            
       ParameterExpression indexExpr = Expression.Parameter(typeof(int), "Index");

       // This parameter represents the value that will be added to a corresponding array element.
       ParameterExpression valueExpr = Expression.Parameter(typeof(int), "Value");

       // This expression represents an array access operation.
       // It can be used for assigning to, or reading from, an array element.
       Expression arrayAccessExpr = Expression.ArrayAccess(
           arrayExpr,
           indexExpr
       );

       // This lambda expression assigns a value provided to it to a specified array element.
       // The array, the index of the array element, and the value to be added to the element
       // are parameters of the lambda expression.
       Expression<Func<int[], int, int, int>> lambdaExpr = Expression.Lambda<Func<int[], int, int, int>>(
           Expression.Assign(arrayAccessExpr, Expression.Add(arrayAccessExpr, valueExpr)),
           arrayExpr,
           indexExpr,
           valueExpr
       );

       // Print out expressions.
       outputBlock.Text += "Array Access Expression:" + "\n";
       outputBlock.Text += arrayAccessExpr.ToString() + "\n";

       outputBlock.Text += "Lambda Expression:" + "\n";
       outputBlock.Text += lambdaExpr.ToString() + "\n";

       outputBlock.Text += "The result of executing the lambda expression:" + "\n";

       // The following statement first creates an expression tree,
       // then compiles it, and then executes it.
       // Parameters passed to the Invoke method are passed to the lambda expression.
       outputBlock.Text += lambdaExpr.Compile().Invoke(new int[] { 10, 20, 30 }, 0, 5) + "\n";

       // This code example produces the following output:
       //
       // Array Access Expression:
       // Array[Index]

       // Lambda Expression:
       // (Array, Index, Value) => (Array[Index] = (Array[Index] + Value))

       // The result of executing the lambda expression:
       // 15

Version Information

Silverlight

Supported in: 5, 4

Platforms

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

Thread Safety

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

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