BlockExpression Class

Definition

Namespace:

System.Linq.Expressions

Assembly:

System.Linq.Expressions.dll

Source:

BlockExpression.cs

Represents a block that contains a sequence of expressions where variables can be defined.

public ref class BlockExpression : System::Linq::Expressions::Expression

public class BlockExpression : System.Linq.Expressions.Expression

type BlockExpression = class
    inherit Expression

Public Class BlockExpression
Inherits Expression

Inheritance

Object

Expression

BlockExpression

Examples

The following code example shows how to create a block expression. The block expression consists of two MethodCallExpression objects and one ConstantExpression object.

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

// The block expression allows for executing several expressions sequentually.
// When the block expression is executed,
// it returns the value of the last expression in the sequence.
BlockExpression blockExpr = Expression.Block(
    Expression.Call(
        null,
        typeof(Console).GetMethod("Write", new Type[] { typeof(String) }),
        Expression.Constant("Hello ")
       ),
    Expression.Call(
        null,
        typeof(Console).GetMethod("WriteLine", new Type[] { typeof(String) }),
        Expression.Constant("World!")
        ),
    Expression.Constant(42)
);

Console.WriteLine("The result of executing the expression tree:");
// The following statement first creates an expression tree,
// then compiles it, and then executes it.
var result = Expression.Lambda<Func<int>>(blockExpr).Compile()();

// Print out the expressions from the block expression.
Console.WriteLine("The expressions from the block expression:");
foreach (var expr in blockExpr.Expressions)
    Console.WriteLine(expr.ToString());

// Print out the result of the tree execution.
Console.WriteLine("The return value of the block expression:");
Console.WriteLine(result);

// This code example produces the following output:
//
// The result of executing the expression tree:
// Hello World!

// The expressions from the block expression:
// Write("Hello ")
// WriteLine("World!")
// 42

// The return value of the block expression:
// 42

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

' The block expression enables you to execute several expressions sequentually.
' When the block expression is executed,
' it returns the value of the last expression in the sequence.
Dim blockExpr As BlockExpression = Expression.Block(
    Expression.Call(
        Nothing,
        GetType(Console).GetMethod("Write", New Type() {GetType(String)}),
        Expression.Constant("Hello ")
       ),
    Expression.Call(
        Nothing,
        GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}),
        Expression.Constant("World!")
        ),
    Expression.Constant(42)
)

Console.WriteLine("The result of executing the expression tree:")
' The following statement first creates an expression tree,
' then compiles it, and then executes it.           
Dim result = Expression.Lambda(Of Func(Of Integer))(blockExpr).Compile()()

' Print the expressions from the block expression.
Console.WriteLine("The expressions from the block expression:")
For Each expr In blockExpr.Expressions
    Console.WriteLine(expr.ToString())
Next

' Print the result of the tree execution.
Console.WriteLine("The return value of the block expression:")
Console.WriteLine(result)

' This code example produces the following output:
'
' The result of executing the expression tree:
' Hello World!

' The expressions from the block expression:
' Write("Hello ")
' WriteLine("World!")
' 42

' The return value of the block expression:
' 42

Remarks

The Block methods can be used to create a BlockExpression.

Properties

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)
Expressions	Gets the expressions in this block.
NodeType	Returns the node type of this expression. Extension nodes should return Extension when overriding this method.
Result	Gets the last expression in this block.
Type	Gets the static type of the expression that this Expression represents.
Variables	Gets the variables defined in this block.

Methods

Accept(ExpressionVisitor)	Dispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall(MethodCallExpression).
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (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(IEnumerable<ParameterExpression>, IEnumerable<Expression>)	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(ExpressionVisitor)	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)