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What are asynchronus streams in C#?
Hammad NasirOverview
In versions of C# prior to 8.0, streams could not be consumed asynchronously. This can now be done, but the following restrictions apply on functions that return asynchronous streams:
- The method is to be declared using the
asyncmodifier. - The method must be of the
IAsyncEnumerable<T>return type, whereTcan be any data type. - The method returns successive elements by using the
yield returnstatement.
The sequence that is returned by such a function is consumed via the await foreach statement.
Example
class Program {
public static async System.Collections.Generic.IAsyncEnumerable<int> GenSeq(int start, int end) {
for (int i = start; i <= end; i++) {
await Task.Delay(1000);
yield return i + 1;
}
}
public static async Task Main() {
await foreach (var num in GenSeq(1, 5)) {
System.Console.WriteLine(num);
}
}
}Output
1
2
3
4
5
In the example above, the GenSeq method generates a sequence of numbers specified by the start and end arguments. These numbers are produced after a delay of 1000 milliseconds or 1 second. The stream produced by the GenSeq function in line 10 is consumed via the await foreach statement, asynchronously.
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