Expression.Lambda Method (Type, Expression, IEnumerable(Of ParameterExpression))
Creates a LambdaExpression by first constructing a delegate type. It can be used when the delegate type is not known at compile time.
Assembly: System.Core (in System.Core.dll)
Public Shared Function Lambda ( delegateType As Type, body As Expression, parameters As IEnumerable(Of ParameterExpression) ) As LambdaExpression
Parameters
- delegateType
-
Type:
System.Type
A Type that represents a delegate signature for the lambda.
- body
-
Type:
System.Linq.Expressions.Expression
An Expression to set the Body property equal to.
- parameters
-
Type:
System.Collections.Generic.IEnumerable(Of ParameterExpression)
An IEnumerable(Of T) that contains ParameterExpression objects to use to populate the Parameters collection.
Return Value
Type: System.Linq.Expressions.LambdaExpressionAn object that represents a lambda expression which has the NodeType property equal to Lambda and the Body and Parameters properties set to the specified values.
| Exception | Condition |
|---|---|
| ArgumentNullException | delegateType or body is null. -or- One or more elements in parameters are null. |
| ArgumentException | delegateType does not represent a delegate type. -or- body.Type represents a type that is not assignable to the return type of the delegate type represented by delegateType. -or- parameters does not contain the same number of elements as the list of parameters for the delegate type represented by delegateType. -or- The Type property of an element of parameters is not assignable from the type of the corresponding parameter type of the delegate type represented by delegateType. |
The object that is returned from this function is of type Expression(Of TDelegate). The LambdaExpression type is used to represent the returned object because the concrete type of the lambda expression is not known at compile time.
The number of parameters for the delegate type represented bydelegateType must equal the length of parameters.
The elements of parameters must be reference equal to the parameter expressions in body.
The Type property of the resulting object is equal to delegateType. If parameters is null, the Parameters property of the resulting object is an empty collection.
The following example demonstrates how to create an expression that represents a lambda expression that adds 1 to the passed argument.
' Add the following directive to your file: ' Imports System.Linq.Expressions ' A parameter for the lambda expression. Dim paramExpr As ParameterExpression = Expression.Parameter(GetType(Integer), "arg") ' This expression represents a lambda expression ' that adds 1 to the parameter value. Dim lambdaExpr As LambdaExpression = Expression.Lambda( Expression.Add( paramExpr, Expression.Constant(1) ), New List(Of ParameterExpression)() From {paramExpr} ) ' Print out the expression. Console.WriteLine(lambdaExpr) ' Compile and run the lamda expression. ' The value of the parameter is 1. Console.WriteLine(lambdaExpr.Compile().DynamicInvoke(1)) ' This code example produces the following output: ' ' arg => (arg +1) ' 2
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1