This documentation is archived and is not being maintained.
ParallelEnumerable::DefaultIfEmpty<TSource> Method (ParallelQuery<TSource>, TSource)
Visual Studio 2010
Returns the elements of the specified parallel sequence or the specified value in a singleton collection if the sequence is empty.
Assembly: System.Core (in System.Core.dll)
[ExtensionAttribute] public: generic<typename TSource> static ParallelQuery<TSource>^ DefaultIfEmpty( ParallelQuery<TSource>^ source, TSource defaultValue )
Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
- Type: System.Linq::ParallelQuery<TSource>
The sequence to return the specified value for if it is empty.
- defaultValue
- Type: TSource
The value to return if the sequence is empty.
Return Value
Type: System.Linq::ParallelQuery<TSource>A sequence that contains defaultValue if source is empty; otherwise, source.
Usage Note
In Visual Basic and C#, you can call this method as an instance method on any object of type ParallelQuery<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).| Exception | Condition |
|---|---|
| ArgumentNullException | source is a null reference (Nothing in Visual Basic). |
| OperationCanceledException | The query was canceled with the token passed in through WithCancellation. |
| AggregateException | One or more exceptions occurred during the evaluation of the query. |
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
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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