What is the Task equivalent to Promise.then()?

Question

With the addition of async / await to TypeScript using Promise(s) can look very syntactically close to Task(s).

Example:

Promise (TS)

public async myAsyncFun(): Promise<T> {
    let value: T = await ...
    return value;
}

Task (C#)

public async Task<T> MyAsyncFun() {
    T value = await ...
    return value;
}

I was wondering if the other way around, there was an equivalent to .then() for Task(s).

Example:

Promise (TS)

Promise<T> promise = ...
promise.then((result: T) => ...do something...);

Answer 1

I've used ContinueWith which can work if you have one or multiple Tasks running.

example:

public async Task<T> MyAsyncFun() {
    T value = await ...
    return value;
}

MyAsyncFun().ContinueWith(...

https://msdn.microsoft.com/en-us/library/dd270696(v=vs.110).aspx

Answer 2

You can create a handy extension method for task continuations to match the javascript .then function. I find it easier to use than .ContinueWith, which has its own set of pitfalls and encumbrances.

public static class TaskExtensions
{
    public static async Task<TV> Then<T,TV>(this Task<T> task, Func<T,TV> then)
    {
        var result = await task;
        return then(result);
    }
}

Then you can use it like so

Task<User> userRecord = GetUserById(123)
Task<string> firstName = userRecord.Then(u => u.FirstName)