BlockExpression Class
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Represents a block that contains a sequence of expressions where variables can be defined.
Assembly: System.Core (in System.Core.dll)
The BlockExpression type exposes the following members.
| Name | Description | |
|---|---|---|
![]() | 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. (Overrides Expression.NodeType.) |
![]() | Result | Gets the last expression in this block. |
![]() | Type | Gets the static type of the expression that this Expression represents. (Overrides Expression.Type.) |
![]() | Variables | Gets the variables defined in this block. |
| Name | Description | |
|---|---|---|
![]() | Accept | Dispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall. (Overrides Expression.Accept(ExpressionVisitor).) |
![]() | Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
![]() | Finalize | Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.) |
![]() | GetHashCode | Serves as a hash function for a particular type. (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 | 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 | 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.) |
The Expression 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) ); outputBlock.Text += "The result of executing the expression tree:" + "\n"; // 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. outputBlock.Text += "The expressions from the block expression:" + "\n"; foreach (var expr in blockExpr.Expressions) outputBlock.Text += expr.ToString() + "\n"; // Print out the result of the tree execution. outputBlock.Text += "The return value of the block expression:" + "\n"; outputBlock.Text += result + "\n"; // 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


