IndexExpression Класс

Определение

public ref class IndexExpression sealed : System::Linq::Expressions::Expression, System::Linq::Expressions::IArgumentProvider

public ref class IndexExpression sealed : System::Linq::Expressions::Expression

public sealed class IndexExpression : System.Linq.Expressions.Expression, System.Linq.Expressions.IArgumentProvider

public sealed class IndexExpression : System.Linq.Expressions.Expression

type IndexExpression = class
    inherit Expression
    interface IArgumentProvider

type IndexExpression = class
    inherit Expression

Public NotInheritable Class IndexExpression
Inherits Expression
Implements IArgumentProvider

Public NotInheritable Class IndexExpression
Inherits Expression

Наследование

Object

Expression

IndexExpression

Реализации

IArgumentProvider

Примеры

В следующем примере кода показано, как создать объект IndexExpression типа и использовать его для изменения значения элемента массива ArrayAccess с помощью метода.

// 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.
Console.WriteLine("Array Access Expression:");
Console.WriteLine(arrayAccessExpr.ToString());

Console.WriteLine("Lambda Expression:");
Console.WriteLine(lambdaExpr.ToString());

Console.WriteLine("The result of executing the lambda expression:");

// 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.
Console.WriteLine(lambdaExpr.Compile().Invoke(new int[] { 10, 20, 30 }, 0, 5));

// 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:
' 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.
Console.WriteLine("Array Access Expression:")
Console.WriteLine(arrayAccessExpr.ToString())

Console.WriteLine("Lambda Expression:")
Console.WriteLine(lambdaExpr.ToString())

Console.WriteLine("The result of executing the lambda expression:")

' 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.
Console.WriteLine(lambdaExpr.Compile().Invoke(New Integer() {10, 20, 30}, 0, 5))

' 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