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Expression<TDelegate> Class

Represents a strongly typed lambda expression as a data structure in the form of an expression tree. This class cannot be inherited.

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

public sealed class Expression<TDelegate> : LambdaExpression

Type Parameters

TDelegate

The type of the delegate that the Expression<TDelegate> represents.

The Expression<TDelegate> type exposes the following members.

  NameDescription
Public propertySupported by Silverlight for Windows PhoneBodyGets the body of the lambda expression. (Inherited from LambdaExpression.)
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 propertyNameGets the name of the lambda expression. (Inherited from LambdaExpression.)
Public propertySupported by Silverlight for Windows PhoneNodeTypeReturns the node type of this Expression. (Inherited from LambdaExpression.)

In Silverlight for Windows Phone Windows Phone OS 7.1, this member is inherited from Expression.NodeType.


In XNA Framework Windows Phone OS 7.0, this member is inherited from Expression.NodeType.
Public propertySupported by Silverlight for Windows PhoneParametersGets the parameters of the lambda expression. (Inherited from LambdaExpression.)
Public propertyReturnTypeGets the return type of the lambda expression. (Inherited from LambdaExpression.)
Public propertyTailCallGets the value that indicates if the lambda expression will be compiled with the tail call optimization. (Inherited from LambdaExpression.)
Public propertySupported by Silverlight for Windows PhoneTypeGets the static type of the expression that this Expression represents. (Inherited from LambdaExpression.)

In Silverlight for Windows Phone Windows Phone OS 7.1, this member is inherited from Expression.Type.


In XNA Framework Windows Phone OS 7.0, this member is inherited from Expression.Type.
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  NameDescription
Protected methodAcceptDispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall. (Inherited from Expression.)
Public methodSupported by Silverlight for Windows PhoneCompile()Compiles the lambda expression described by the expression tree into executable code and produces a delegate that represents the lambda expression.
Public methodCompile(DebugInfoGenerator)Produces a delegate that represents the lambda expression.
Public methodCompileToMethod(MethodBuilder)Compiles the lambda into a method definition. (Inherited from LambdaExpression.)
Public methodCompileToMethod(MethodBuilder, DebugInfoGenerator)Compiles the lambda into a method definition and custom debug information. (Inherited from LambdaExpression.)
Public methodSupported by Silverlight for Windows PhoneEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodSupported by Silverlight for Windows PhoneFinalizeAllows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Public methodSupported by Silverlight for Windows PhoneGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodSupported by Silverlight for Windows PhoneGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodSupported by Silverlight for Windows PhoneMemberwiseCloneCreates 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 methodSupported by Silverlight for Windows PhoneToStringReturns 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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When a lambda expression is assigned to a variable, field, or parameter whose type is Expression<TDelegate>, the compiler emits instructions to build an expression tree.

NoteNote:

A conversion from a lambda expression to type Expression<D> (Expression(Of D) in Visual Basic) exists if a conversion from the lambda expression to a delegate of type D exists. However, the conversion may fail, for example, if the body of the lambda expression is a block. This means that delegates and expression trees behave similarly with regard to overload resolution.

The expression tree is an in-memory data representation of the lambda expression. The expression tree makes the structure of the lambda expression transparent and explicit. You can interact with the data in the expression tree just as you can with any other data structure.

The ability to treat expressions as data structures enables APIs to receive user code in a format that can be inspected, transformed, and processed in a custom manner. For example, the LINQ to SQL data access implementation uses this facility to translate expression trees to Transact-SQL statements that can be evaluated by the database.

Many standard query operators defined in the Queryable class have one or more parameters of type Expression<TDelegate>.

The NodeType of an Expression<TDelegate> is Lambda.

Use the Lambda<TDelegate>(Expression, IEnumerable<ParameterExpression>) or Lambda<TDelegate>(Expression, ParameterExpression[]) method to create an Expression<TDelegate> object.

The following code example demonstrates how to represent a lambda expression both as executable code in the form of a delegate and as data in the form of an expression tree. It also demonstrates how to turn the expression tree back into executable code by using the Compile method.



      // Lambda expression as executable code.
      Func<int, bool> deleg = i => i < 5;
      // Invoke the delegate and display the output.
      outputBlock.Text += String.Format("deleg(4) = {0}", deleg(4)) + "\n";

      // Lambda expression as data in the form of an expression tree.
      System.Linq.Expressions.Expression<Func<int, bool>> expr = i => i < 5;
      // Compile the expression tree into executable code.
      Func<int, bool> deleg2 = expr.Compile();
      // Invoke the method and print the output.
      outputBlock.Text += String.Format("deleg2(4) = {0}", deleg2(4)) + "\n";

      /*  This code produces the following output:

          deleg(4) = True
          deleg2(4) = True
      */



Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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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