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Enumerable.Empty(Of TResult) Method

Returns an empty IEnumerable(Of T) that has the specified type argument.

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

'Declaration
Public Shared Function Empty(Of TResult) As IEnumerable(Of TResult)

Type Parameters

TResult

The type to assign to the type parameter of the returned generic IEnumerable(Of T).

Return Value

Type: System.Collections.Generic.IEnumerable(Of TResult)
An empty IEnumerable(Of T) whose type argument is TResult.

The Empty(Of TResult) method caches an empty sequence of type TResult. When the object it returns is enumerated, it yields no elements.

In some cases, this method is useful for passing an empty sequence to a user-defined method that takes an IEnumerable(Of T). It can also be used to generate a neutral element for methods such as Union. See the Example section for an example of this use of Empty(Of TResult).

The following code example demonstrates how to use Empty(Of TResult) to generate an empty IEnumerable(Of T).

' Create an empty sequence. 
Dim empty As IEnumerable(Of Decimal) = Enumerable.Empty(Of Decimal)()

The following code example demonstrates a possible application of the Empty(Of TResult) method. The Aggregate method is applied to a collection of string arrays. The elements of each array in the collection are added to the resulting IEnumerable(Of T) only if that array contains four or more elements. Empty(Of TResult) is used to generate the seed value for Aggregate because if no array in the collection has four or more elements, only the empty sequence is returned.

        ' Create three string arrays. 
        Dim names1() As String = _
            {"Hartono, Tommy"}
        Dim names2() As String = _
            {"Adams, Terry", "Andersen, Henriette Thaulow", "Hedlund, Magnus", "Ito, Shu"}
        Dim names3() As String = _
            {"Solanki, Ajay", "Hoeing, Helge", "Andersen, Henriette Thaulow", "Potra, Cristina", "Iallo, Lucio"}

        ' Create a List that contains 3 elements, where 
        ' each element is an array of strings. 
        Dim namesList As New List(Of String())(New String()() {names1, names2, names3})

        ' Select arrays that have four or more elements and union 
        ' them into one collection, using Empty() to generate the  
        ' empty collection for the seed value. 
        Dim allNames As IEnumerable(Of String) = _
            namesList.Aggregate(Enumerable.Empty(Of String)(), _
                                Function(current, nextOne) _
                                    IIf(nextOne.Length > 3, current.Union(nextOne), current))

        Dim output As New System.Text.StringBuilder
        For Each name As String In allNames
            output.AppendLine(name)
        Next 

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

        ' This code produces the following output: 
        
        ' Adams, Terry 
        ' Andersen, Henriette Thaulow 
        ' Hedlund, Magnus 
        ' Ito, Shu 
        ' Solanki, Ajay 
        ' Hoeing, Helge 
        ' Potra, Cristina 
        ' Iallo, Lucio

.NET Framework

Supported in: 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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