Why can Task.WhenAll take any number of Task arguments?

Question

While reviewing Async and Await, I noticed that Task.WhenAll could be called with any number of parameters:

Threading.Tasks.Task.WhenAll(New Threading.Tasks.Task(New Action(Sub() Console.WriteLine("Hello"))),
                             New Threading.Tasks.Task(New Action(Sub() Console.WriteLine("Hello"))),
                             New Threading.Tasks.Task(New Action(Sub() Console.WriteLine("Hello"))),
                             New Threading.Tasks.Task(New Action(Sub() Console.WriteLine("Hello"))),
                             New Threading.Tasks.Task(New Action(Sub() Console.WriteLine("Hello"))))

Why does this work, but methods like Array.Reverse do not allow you to pass any number of parameters?

Possible duplicate of [Why use the params keyword?](http://stackoverflow.com/questions/7580277/why-use-the-params-keyword) — TheLethalCoder, Nov 29 '16 at 16:53

score 0 · Accepted Answer · edited May 23 '17 at 12:30

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Turns out that after looking at the code on the .Net Reference Source site, specifically the overload with an array of Tasks, and after looking at this SO post, I found that the params keyword (ParamArray in VB.Net) allows you to pass no arguments, any number of comma separated arguments of the specified type, or an array of the specified type.

You can think of it like destructuring an Array in Javascript or the args array in Python.

edited May 23 '17 at 12:30

Community

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answered Nov 29 '16 at 16:47

Colin Hartwig

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This looks like JS `...theArgs` to me: String [from metadata] ... `public static string Format(string format, params object[] args);` – 15ee8f99-57ff-4f92-890c-b56153 Nov 29 '16 at 16:50
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This also applies to methods such as `Path.Combine` from the `System.IO` namespace, you'll come across this often. – ColinM Nov 29 '16 at 16:51
As a rule, when in doubt, right-click on any .NET method or class in VS and select "Go to Definition". Careful with `params object[]` though, when you define your own: You can get unexpected results with overloads. – 15ee8f99-57ff-4f92-890c-b56153 Nov 29 '16 at 16:52

Why can Task.WhenAll take any number of Task arguments?

1 Answers1