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MSDN Library

ParallelEnumerable::DefaultIfEmpty<TSource> Method (ParallelQuery<TSource>)

Returns the elements of the specified parallel sequence or the type parameter's default value in a singleton collection if the sequence is empty.

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

[ExtensionAttribute]
public:
generic<typename TSource>
static ParallelQuery<TSource>^ DefaultIfEmpty(
	ParallelQuery<TSource>^ source
)

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Linq::ParallelQuery<TSource>

The sequence to return a default value for if it is empty.

Return Value

Type: System.Linq::ParallelQuery<TSource>
A sequence that contains default(TSource) 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).

ExceptionCondition
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.

.NET Framework

Supported in: 4.6, 4.5, 4

.NET Framework Client Profile

Supported in: 4

.NET for Windows Phone apps

Supported in: Windows Phone 8.1

Portable Class Library

Supported in: Portable Class Library
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