Class First

Namespace

Bonsai.Reactive

Assembly

Bonsai.Core.dll

Represents an operator that returns the first element of an observable sequence.

If the sequence has no elements, First will terminate with an error.

Tip

If you are interested in finding the first element that meets some criteria, consider using the Condition operator before First.

Example

Use First to retrieve the first element of a sequence.

Alternative

Use Take to retrieve one or more elements from the start of the sequence.

Warning

There are subtle but important differences between using the First operator and Take(1):

• When the source sequence has no elements, Take(1) will complete successfully, while First will throw an error.
• When the source sequence emits the first element, Take(1) will immediately cancel the subscription to the source sequence before emitting the notification. First, on the other hand, will emit the notification and only afterwards cancel the subscription to the source sequence.

Use FirstOrDefault to retrieve the first element or return a default element if the sequence is empty.

public class First : Combinator

Inheritance

object

Combinator

First

Inherited Members

object.ToString()

object.Equals(object)

object.Equals(object, object)

object.ReferenceEquals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

Methods

Process<TSource>(IObservable<TSource>)

Returns the first element of an observable sequence.