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BlockExpression Class

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

System.Object
  System.Linq.Expressions.Expression
    System.Linq.Expressions.BlockExpression

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

public class BlockExpression : Expression

The BlockExpression type exposes the following members.

  NameDescription
Public propertyCanReduceIndicates 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.)
Public propertyExpressionsGets the expressions in this block.
Public propertyNodeTypeReturns the node type of this expression. Extension nodes should return Extension when overriding this method. (Overrides Expression.NodeType.)
Public propertyResultGets the last expression in this block.
Public propertyTypeGets the static type of the expression that this Expression represents. (Overrides Expression.Type.)
Public propertyVariablesGets the variables defined in this block.
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  NameDescription
Protected methodAcceptDispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall. (Overrides Expression.Accept(ExpressionVisitor).)
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodReduceReduces 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.)
Public methodReduceAndCheckReduces 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.)
Public methodReduceExtensionsReduces 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.)
Public methodToStringReturns a textual representation of the Expression. (Inherited from Expression.)
Public methodUpdateCreates 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.
Protected methodVisitChildrenReduces 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.)
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The Block methods can be used to create a BlockExpression.

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


.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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