Enumerable.DefaultIfEmpty<'TSource> Method (IEnumerable<'TSource>, 'TSource)
Returns the elements of the specified sequence or the specified value in a singleton collection if the sequence is empty.
Assembly: System.Core (in System.Core.dll)
static member DefaultIfEmpty<'TSource> : source:IEnumerable<'TSource> * defaultValue:'TSource -> IEnumerable<'TSource>
The sequence to return the specified value for if it is empty.
The value to return if the sequence is empty.
Return ValueType: System.Collections.Generic.IEnumerable<'TSource>
An IEnumerable<'T> that contains defaultValue if source is empty; otherwise, source.
The type of the elements of source.
This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.
This method can be used to produce a left outer join when it is combined with the GroupJoin<'TOuter, 'TInner, 'TKey, 'TResult>) method.
Available since 8
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Available since 8.1