public:
generic <typename TResult>
static System::Collections::Generic::IEnumerable<TResult> ^ Empty();
public static System.Collections.Generic.IEnumerable<TResult> Empty<TResult> ();
static member Empty : unit -> seq<'Result>
Public Function Empty(Of TResult) () As IEnumerable(Of TResult)
TResult
下面的代码示例演示如何使用
Empty<TResult>()
生成空
IEnumerable<T>
。
IEnumerable<decimal> empty = Enumerable.Empty<decimal>();
' Create an empty sequence.
Dim empty As IEnumerable(Of Decimal) = Enumerable.Empty(Of Decimal)()
下面的代码示例演示 了 方法的
Empty<TResult>()
可能应用。 方法
Aggregate
应用于字符串数组的集合。 仅当该数组包含四个或更多个元素时，集合中每个数组的元素才会添加到生成的
IEnumerable<T>
。
Empty
用于生成 的
Aggregate
种子值，因为如果集合中没有数组包含四个或更多个元素，则只返回空序列。
string[] names1 = { "Hartono, Tommy" };
string[] names2 = { "Adams, Terry", "Andersen, Henriette Thaulow",
"Hedlund, Magnus", "Ito, Shu" };
string[] names3 = { "Solanki, Ajay", "Hoeing, Helge",
"Andersen, Henriette Thaulow",
"Potra, Cristina", "Iallo, Lucio" };
List<string[]> namesList =
new List<string[]> { names1, names2, names3 };
// Only include arrays that have four or more elements
IEnumerable<string> allNames =
namesList.Aggregate(Enumerable.Empty<string>(),
(current, next) => next.Length > 3 ? current.Union(next) : current);
foreach (string name in allNames)
Console.WriteLine(name);
This code produces the following output:
Adams, Terry
Andersen, Henriette Thaulow
Hedlund, Magnus
Ito, Shu
Solanki, Ajay
Hoeing, Helge
Potra, Cristina
Iallo, Lucio
' 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)
' Display the output.
Console.WriteLine(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
方法
Empty<TResult>()
缓存 类型
TResult
为 的空序列。 当枚举它返回的对象时，它不生成任何元素。
在某些情况下，此方法可用于将空序列传递给采用
IEnumerable<T>
的用户定义方法。 它还可用于为 等
Union
方法生成中性元素。 有关此用法
Empty<TResult>()
的示例，请参阅示例部分。
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