Difference between await and using discards

Question

What is the difference between the below two lines.

await SkillReporterDatabase.Database.SaveAsync(someObject);

_ = SkillReporterDatabase.Database.SaveAsync(someObject);

Which one is preferred? Sometimes when I face some issue with await, I use _ = and it solves the problem. I couldn't see any resources online which explains the difference between these two.

Answer 1

The difference is that the discard (_) doesn't care about what happens in SaveAsync once it becomes asynchronous, which it presumably does do; this has two important side effects:

1. you won't know if the save failed
2. if you perform any other operations via Database, you're probably going to be running overlapped operations on a single context/connection, which is not usually a supported scenario

So in this case, await is probably preferred. There are times when it is OK to discard a task, but that usually means when you start something in the background that has no further interaction with the current flow.

Answer 2

Without the await, later operations will not be blocked by the SaveAsync call and will therefore run concurrently. The discard is just saving the Task (a task is conceptually a bit like a progress bar), not the result of the Task the way the awaited call is.

so SaveAsync returns a Task (like a promise in JavaScript). Calling await on that Task will block until the task completes and returns a result. Not calling await and instead just throwing away the Task is like throwing away a pointer in C++ -- your program will start the task and then forget about it -- it may still complete but the code in this method will never find out whether it does or not.