BehaviorSubject.First() obsolete, what is the alternative?

.net, system.reactive

Solution

With `BehaviorSubject<T>` you are guaranteed* to have a `First` value always available.

However, `IObservable<T>` query operators can't work under that assumption in general, so the `Obsolete` attribute was added to drive people towards asynchronous methods like `FirstAsync` - helping them to "fall into the pit of success".

Because of the special case of `BehaviorSubject<T>` always having a value set, it has a thread safe `Value` property. So, assuming that you have something like this:

var subject = new BehaviorSubject<string>("Some value");

Then you can do this:

var current = subject.Value;

*Attempting to acess the value of a `BehaviorSubject<T>` instance after its `Dispose` method has been called, whether by the `Value` property or a query operator like `FirstAsync`, will cause an `ObjectDisposedException` to be thrown.

Problem

So I have a `BehaviorSubject<string>` which I wish to use for a property. I have been using the blocking `First()` method to get the current value that the `BehaviorSubject` holds in a property getter. The `First()` operation is now obsolete, so what is the new way to achieve this?

Original source