,System.Boolean,-0,System.Threading.CancellationToken)}

SingleElementWitness(Func?, bool, T?, CancellationToken) constructor¶

Defined in

Type: SingleElementWitness Namespace: ReactiveUI.Primitives.Async.Advanced Assembly: ReactiveUI.Primitives.Async.Core.dll

Applies to

net10.0, net10.0-browserwasm1.0, net10.0-desktop1.0, net9.0, net9.0-browserwasm1.0, net9.0-desktop1.0, net8.0, net8.0-ios17.5, net8.0-maccatalyst17.5, net8.0-macos14.2, net8.0-macos14.5, net8.0-tvos17.2, netstandard2.1, net462, net481

public SingleElementWitness(Func<T, bool>? predicate, bool requireExactlyOne, T? defaultValue, CancellationToken cancellationToken)

View source

Summary: Shared observer used by both SingleAsync and SingleOrDefaultAsync. The two operator surfaces previously held near-identical observer classes; the only behavioural difference is whether an empty sequence throws or returns a caller-supplied default. That difference is now a single flag on this type, so the OnNext / OnErrorResume / OnCompleted bodies live in one place.

Parameters

Name	Type	Description
`predicate`	Func?	An optional predicate to filter elements; `null` matches all elements.
`requireExactlyOne`	bool	When `true` (the `SingleAsync` shape), an empty sequence completes the result task with an InvalidOperationException. When `false` (the `SingleOrDefaultAsync` shape), an empty sequence resolves the result task with `defaultValue`.
`defaultValue`	`T?`	The value to return on empty when `requireExactlyOne` is `false`.
`cancellationToken`	CancellationToken	A cancellation token for the operation.