Curious C# using statement expansion

Question

I\'ve run ildasm to find that this:

    using(Simple simp = new Simple())
    {
        Console.WriteLine(\"here\");
    }

generates IL cod

Answer 1

It appears that your comment:

"If there is some fear that some intervening steps might come between the Simple constructor and the beginning of the try block, then that would really be a problem because then an exception might be thrown that would prevent the finally block from executing at all."

is possibly dead on. See:

Atomicity & Asynchronous Exception Failures

I also want to note the issue(s) with WCF and using:

Avoiding Problems with the Using Statement and WCF Service Proxies which references:

Avoiding Problems with the Using Statement

Answer 2

No, the finally block will ALWAYS be executed. You may not be getting the object from a new but from some other function that returns your object - and it might return NULL. using() is your friend!

dss539 was kind enough to suggest I include his note:

using(Simple simp = null) 

is yet another reason that the expansion must check for null first.

Answer 3

The code must be translated this way to avoid possible NullReferenceException when disposing the object. As per C# language reference, the using statement accepts not only a local variable declaration as its first nonterminal resource_acquisition symbol, but any expression. Consider the following code:

DisposableType @object = null;
using(@object) {
    // whatever
}

Clearly, unless null-conditional @object?.Dispose() in the finnaly block, an exception would ensue. The null check is superfluous only when the expression is of a non-nullable value type (non-nullable struct). And indeed, according to the aforementioned language reference it is absent in such case.

Answer 4

using(Simple simp = null) is yet another reason that the expansion must check for null first.

Answer 5

MSDN on the using statement.

What I think is strange is that it doesn't expand to:

Simple simp = new Simple();
Simple __compilergeneratedtmpname = simp;
try
{
    Console.WriteLine("here");
}
finally
{
    if(__compilergeneratedtmpname != null)
    {
        __compilergeneratedtmpname.Dispose();
    }
}