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Expression.ArrayAccess Method (Expression, IEnumerable(Of Expression))

Creates an IndexExpression to access a multidimensional array.

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

'Declaration
Public Shared Function ArrayAccess ( _
	array As Expression, _
	indexes As IEnumerable(Of Expression) _
) As IndexExpression

Parameters

array
Type: System.Linq.Expressions.Expression
An expression that represents the multidimensional array.
indexes
Type: System.Collections.Generic.IEnumerable(Of Expression)
An IEnumerable(Of T) containing expressions used to index the array.

The expression that represents the array can be obtained by using the MakeMemberAccess method, or through NewArrayBounds or NewArrayInit.

The following code example shows how to change the value of an element in a multidimensional array 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 two-dimensional array.
        Dim arrayExpr As ParameterExpression = Expression.Parameter(GetType(Integer(,)), "Array")

        ' This parameter expression represents a first array index.            
        Dim firstIndexExpr As ParameterExpression = Expression.Parameter(GetType(Integer), "FirstIndex")
        ' This parameter expression represents a second array index.            
        Dim secondIndexExpr As ParameterExpression = Expression.Parameter(GetType(Integer), "SecondIndex")

        ' The list of indexes.
        Dim indexes As List(Of Expression) = New List(Of Expression) From
            {firstIndexExpr, secondIndexExpr}

        ' 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 access operation to a multidimensional array.
        ' It can be used for assigning to, or reading from, an array element.
        Dim arrayAccessExpr As Expression = Expression.ArrayAccess(
            arrayExpr,
            indexes
        )

        ' 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, Integer)) =
            Expression.Lambda(Of Func(Of Integer(,), Integer, Integer, Integer, Integer))(
                Expression.Assign(arrayAccessExpr, Expression.Add(arrayAccessExpr, valueExpr)),
                arrayExpr,
                firstIndexExpr,
                secondIndexExpr,
                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.
        Dim sampleArray = {{10, 20, 30},
                               {100, 200, 300}}
        outputBlock.Text &= lambdaExpr.Compile().Invoke(sampleArray, 1, 1, 5) & vbCrLf

        ' This code example produces the following output:
        '
        ' Array Access Expression:
        ' Array[FirstIndex, SecondIndex]

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

        ' The result of executing the lambda expression:
        ' 205



Silverlight

Supported in: 5, 4

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

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