Syntax for using declaration without variable [duplicate]

Question

Consider a disposable with side effects in the constructor:

public class MyDisposable : IDisposable
{
    public MyDisposable()
    {
        // Some side effects
        ...
    }

    public void Dispose()
    {
        ...
    }
}

If I'm only interested in the side effects I can, in some method, use the class like so:

using var _ = new MyDisposable();
using var __ = new MyDisposable();
using var ___ = new MyDisposable();

Is there some syntax to avoid declaring the variables as they are unused? Something like:

using new MyDisposable();
using new MyDisposable();
using new MyDisposable();

I'm only interested in if there is such a syntax. I'm not looking for a way to restructure the code into a more sane approach.

I mean, by your own admission this isn’t sane, so why would special syntax exist to support it? — Konrad Rudolph
– Konrad Rudolph, Commented Jan 19, 2022 at 14:40
Side effects are already a code smell, but being only interested in size effects is the extreme version. You should definitely refactor to another solution, because this doesn't sound like a good design. — JHBonarius
– JHBonarius, Commented Jan 19, 2022 at 14:54
@JHBonarius I can think of an use here: C++-like scope locks. public MyDisposable() { Monitor.Enter(o); } public void Dispose(){ Monitor.Exit(o); } That may come in useful in one form or another. — PMF
– PMF, Commented Jan 19, 2022 at 15:03

Olivier Jacot-Descombes · Accepted Answer · 2022-01-19 14:50:14Z

1

The using statement works without variable declation:

using (new MyDisposable()) {
    Console.WriteLine("in using");
}

You can test it with this class:

public class MyDisposable : IDisposable
{
    public void Dispose()
    {
        Console.WriteLine("Dispose");
    }
}

and this console app:

Console.WriteLine("Start");
using (new MyDisposable()) {
    Console.WriteLine("in using");
}
Console.WriteLine("End");
Console.ReadKey();

It prints:

Start
in using
Dispose
End

answered Jan 19, 2022 at 14:50

Olivier Jacot-Descombes

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