Sorry if this question has been asked before, but I can't find a duplicate. Also sorry for asking too many questions lately! I am probably searching for a custom Observable.Using
method, that is not restricted to disposable resources. What I have is a cold IObservable
that maintains some internal state, for example a Random
instance. This instance should be bound not with the IObservable
itself, but with each of its subscriptions. Each subscriber should use a different instance of this resource. Take a look for example to the GetRandomNumbers
method below:
static IObservable<int> GetRandomNumbers()
{
var random = new Random(0);
return Observable
.Interval(TimeSpan.FromMilliseconds(100))
.Select(x => random.Next(1, 10))
.Take(10);
}
This method generates 10 random numbers. The RNG is a Random
instance initialized with a constant seed, so it should produce always the same 10 numbers. But alas it doesn't:
var stream = GetRandomNumbers();
Console.WriteLine($"Results A: {String.Join(", ", await stream.ToArray())}");
Console.WriteLine($"Results B: {String.Join(", ", await stream.ToArray())}");
Output:
Results A: 7, 8, 7, 6, 2, 6, 9, 4, 9, 3
Results B: 3, 5, 6, 5, 9, 1, 8, 9, 7, 3
Each subscriber of the stream
observable gets a different set of numbers! What happens is that the same Random
instance is used by all subscribers. This is not only undesirable, but it also creates the risk of corrupting the internal state of the object, since the Random
class is not thread-safe.
My attempt to solve this problem was to use the Using
operator, that has a Func<TResource> resourceFactory
parameter:
static IObservable<int> GetRandomNumbers()
{
return Observable.Using(() => new Random(0), random =>
Observable
.Interval(TimeSpan.FromMilliseconds(100))
.Select(x => random.Next(1, 10))
.Take(10)
);
}
This would be a perfect solution if the Random
was disposable (I tested it with a disposable class and worked as expected), but it's not, and so the code doesn't compile:
The type 'System.Random' cannot be used as type parameter 'TResource' in the generic type or method 'Observable.Using<TResult, TResource>(Func, Func<TResource, IObservable>)'. There is no implicit reference conversion from 'System.Random' to 'System.IDisposable'.
Could you suggest a solution to this problem?
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