Expression.Assign(Expression, Expression) Metodo

Definizione

Spazio dei nomi:

System.Linq.Expressions

Assembly:

System.Linq.Expressions.dll

Origine:

BinaryExpression.cs

Crea un oggetto BinaryExpression che rappresenta un'operazione di assegnazione.

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

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

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

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

Parametri

left

Expression

Oggetto Expression su cui impostare la proprietà Left.

right

Expression

Oggetto Expression su cui impostare la proprietà Right.

Restituisce

BinaryExpression

Oggetto BinaryExpression la cui proprietà NodeType è uguale a Assign e le cui proprietà Left e Right sono impostate sui valori specificati.

Esempio

Nell'esempio di codice seguente viene illustrato come creare un'espressione che rappresenta un'operazione di assegnazione.

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

// To demonstrate the assignment operation, we create a variable.
ParameterExpression variableExpr = Expression.Variable(typeof(String), "sampleVar");

// This expression represents the assignment of a value
// to a variable expression.
// It copies a value for value types, and
// copies a reference for reference types.
Expression assignExpr = Expression.Assign(
    variableExpr,
    Expression.Constant("Hello World!")
    );

// The block expression allows for executing several expressions sequentually.
// In this block, we pass the variable expression as a parameter,
// and then assign this parameter a value in the assign expression.
Expression blockExpr = Expression.Block(
    new ParameterExpression[] { variableExpr },
    assignExpr
    );

// Print out the assign expression.
Console.WriteLine(assignExpr.ToString());

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

// This code example produces the following output:
//
// (sampleVar = "Hello World!")
// Hello World!

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

' To demonstrate the assignment operation, create a variable.
Dim variableExpr As ParameterExpression = Expression.Variable(GetType(String), "sampleVar")

' This expression represents the assignment of a value
' to a variable expression.
' It copies a value for value types, and it
' copies a reference for reference types.
Dim assignExpr As Expression = Expression.Assign(
    variableExpr,
    Expression.Constant("Hello World!")
    )

' The block expression allows for executing several expressions sequentually.
' In this block, you pass the variable expression as a parameter,
' and then assign this parameter a value in the assign expression.
Dim blockExpr As Expression = Expression.Block(
      New ParameterExpression() {variableExpr}, assignExpr
      )

' Print the assign expression.
Console.WriteLine(assignExpr.ToString())

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

' This code example produces the following output:
'
' (sampleVar = "Hello World!")
' Hello World!

Commenti

L'espressione Assign copia un valore per i tipi di valore e copia un riferimento per i tipi di riferimento.