• Article

Expression.ArrayAccess Method (Expression, array<Expression[])

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Creates an IndexExpression to access an array.

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

Syntax

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

public static IndexExpression ArrayAccess(
    Expression array,
    params Expression[] indexes
)

Parameters

Remarks

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

For multidimensional arrays, use the ArrayAccess method.

Examples

The following code example shows how 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.