'await' on left side of assigment

Question

I was looking at some of the example code on Microsoft Playwright and in the example code, there is this bit

public static async Task Main()
{
    using var playwright = await Playwright.CreateAsync();
    await using var browser = await playwright.Chromium.LaunchAsync();
    var page = await browser.NewPageAsync();
    await page.GotoAsync("https://playwright.dev/dotnet");
    await page.ScreenshotAsync(new PageScreenshotOptions { Path = "screenshot.png" });
}

What does the first await in line 4 do? I've tried searching for it but I can't find any documentation on it.

The `await using` syntax means the disposal uses `DisposeAsync` instead of `Dispose`. — Matthew, Nov 18 '21 at 12:39
Does this answer your question? [C# 8 understanding await using syntax](https://stackoverflow.com/questions/58791938/c-sharp-8-understanding-await-using-syntax) — Andrew McClement, Nov 18 '21 at 12:43
There's not really an await on the left side of the assignment. You could split this up into two lines for clarity `var browser = await playwright.Chromium.LaunchAsync();` and then `await using browser;` — DavidG, Nov 18 '21 at 12:44
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Guru Stron · Answer 1 · 2021-11-18T12:50:02.043

If you are talking about:

await using var browser = await playwright.Chromium.LaunchAsync();

line, then this is not just an assignment but two features added in C# 8 combined - asynchronous disposable:

Starting with C# 8.0, the language supports asynchronous disposable types that implement the System.IAsyncDisposable interface. You use the await using statement to work with an asynchronously disposable object.

and using declarations:

A using declaration is a variable declaration preceded by the using keyword. It tells the compiler that the variable being declared should be disposed at the end of the enclosing scope.

score 0 · Answer 2 · answered Nov 18 '21 at 12:43

From the docs:

You use the await using statement to work with an asynchronously disposable object, that is, an object of a type that implements an IAsyncDisposable interface. For more information, see the Using async disposable section of the Implement a DisposeAsync method article.

IAsyncDisposable is used for releasing unmanaged resources in asynchronous manner.

'await' on left side of assigment

2 Answers2