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Enumerable.AsEnumerable(Of TSource) Method

Returns the input typed as IEnumerable(Of T).

Namespace:  System.Linq
Assemblies:   System.Linq (in System.Linq.dll)
  System.Core (in System.Core.dll)

'Declaration
<ExtensionAttribute> _
Public Shared Function AsEnumerable(Of TSource) ( _
	source As IEnumerable(Of TSource) _
) As IEnumerable(Of TSource)

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable(Of TSource)

The sequence to type as IEnumerable(Of T).

Return Value

Type: System.Collections.Generic.IEnumerable(Of TSource)
The input sequence typed as IEnumerable(Of T).

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable(Of TSource). When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

The AsEnumerable(Of TSource)(IEnumerable(Of TSource)) method has no effect other than to change the compile-time type of source from a type that implements IEnumerable(Of T) to IEnumerable(Of T) itself.

AsEnumerable(Of TSource)(IEnumerable(Of TSource)) can be used to choose between query implementations when a sequence implements IEnumerable(Of T) but also has a different set of public query methods available. For example, given a generic class Table that implements IEnumerable(Of T) and has its own methods such as Where, Select, and SelectMany, a call to Where would invoke the public Where method of Table. A Table type that represents a database table could have a Where method that takes the predicate argument as an expression tree and converts the tree to SQL for remote execution. If remote execution is not desired, for example because the predicate invokes a local method, the AsEnumerable(Of TSource) method can be used to hide the custom methods and instead make the standard query operators available.

The following code example demonstrates how to use AsEnumerable(Of TSource)(IEnumerable(Of TSource)) to hide a type's custom Where method when the standard query operator implementation is desired.

    Dim output As New System.Text.StringBuilder

    ' A custom class. 
    Class Clump(Of T)
        Inherits List(Of T)

        ' Constructor. 
        Public Sub New(ByVal collection As System.Collections.Generic.IEnumerable(Of T))
            MyBase.New(collection)
        End Sub 

        ' Custom implementation of Where(). 
        Function Where(ByVal predicate As Func(Of T, Boolean)) As IEnumerable(Of T)
            output.AppendLine("In Clump's implementation of Where().")
            Return Enumerable.Where(Me, predicate)
        End Function 
    End Class 

    Sub AsEnumerableEx1()
        ' Create a new Clump(Of T) object. 
        Dim fruitClump As New Clump(Of String)(New String() _
                                               {"apple", "passionfruit", "banana", _
                                                "mango", "orange", "blueberry", _
                                                "grape", "strawberry"})

        ' First call to Where(): 
        ' Call Clump's Where() method with a predicate. 
        Dim query1 As IEnumerable(Of String) = _
            fruitClump.Where(Function(fruit) fruit.Contains("o"))
        output.AppendLine("query1 has been created." & vbCrLf)

        ' Second call to Where(): 
        ' First call AsEnumerable() to hide Clump's Where() method and thereby 
        ' force System.Linq.Enumerable's Where() method to be called. 
        Dim query2 As IEnumerable(Of String) = _
            fruitClump.AsEnumerable().Where(Function(fruit) fruit.Contains("o"))
        output.AppendLine("query2 has been created.")

        ' Display the output.
        MsgBox(output.ToString())
    End Sub 

    ' This code produces the following output: 
    
    ' In Clump's implementation of Where(). 
    ' query1 has been created. 
    
    ' query2 has been created.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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