using statement equivalent

Al Beback

I've been looking around for an answer to this puzzling question, but so far no luck: What's the compiler's try/finally equivalent of this code:

using (new SomeIDisposableClass())
{
SomeCode();
}

Thanks!

ShamWow

Lost User

There's a CodeProject-article[^] that shows how it is translated :)

I are Troll :suss:

J4amieC

IDisposable disposable = null;
try
{
disposable = new SomeIDisposableClass()
SomeCode();
}
finally
{
disposable.Dispose();
}

Al Beback

Thanks for the quick response, but that article doesn't address my specific example where a variable is not explicitly declared inside the using statement.

ShamWow

dan sh

Why and when would you write a code like that? As far as its equivalent is concerned, just see the IL through ILDAsm or reflector and it would make things a bit clear. :)

modified on Monday, June 14, 2010 11:55 AM

Al Beback

Sounds logical, although I would imagine the compiler would also add an extra check for whether "disposable" is null inside the finally block. It's interesting that none of the examples you see out there for the using statement ever mention that if you don't assign your IDisposable type to an explicitly declared variable, the compiler will do it for you behind the scenes. Thanks.

ShamWow

Lost User

Al Beback wrote:

that article doesn't address my specific example where a variable is not explicitly declared inside the using statement.

Ah, my bad; it does almost the same the same thing, with the difference that you don't have a reference to your class. It still creates a class, disposing it in the finally.

public static void Main(string[] args)
{
using (new SomeIDisposableClass())
{
Console.WriteLine("Hello World!");
}
Console.ReadKey(true);
}

..translates to..

.method public hidebysig static
void Main(string[] args) cil managed
{
.entrypoint
.maxstack 2
.locals init (
[0] class using_test.SomeIDisposableClass CS$3$0000,
[1] bool CS$4$0001)
L_0000: nop
L_0001: newobj instance void
using_test.SomeIDisposableClass::.ctor()
L_0006: stloc.0
L_0007: nop
L_0008: ldstr "Hello World!"
L_000d: call void [mscorlib]System.Console::WriteLine(string)
L_0012: nop
L_0013: nop
L_0014: leave.s L_0026
L_0016: ldloc.0
L_0017: ldnull
L_0018: ceq
L_001a: stloc.1
L_001b: ldloc.1
L_001c: brtrue.s L_0025
L_001e: ldloc.0
L_001f: callvirt instance void
[mscorlib]System.IDisposable::Dispose()
L_0024: nop
L_0025: endfinally
L_0026: nop
L_0027: ldc.i4.1
L_0028: call valuetype
[mscorlib]System.ConsoleKeyInfo
[mscorlib]System.Console::ReadKey(bool)
L_002d: pop
L_002e: ret
.try L_0007 to L_0016 finally handler L_0016 to L_0026
}

I are Troll :suss:

Al Beback · modified on Monday, June 14, 2010 11:55 AM

d@nish wrote:

Why and when would you write a code like that?

When you're interested in keeping track of when "SomeCode" begins and ends -- for logging, profiling, etc.

ShamWow

dan sh

Use interceptor pattern for that. Check out Enterprise Library's Policy Injection Block to see how logging can be done before and after method call. (Search LogCallHandler)

Lost User

Wow, everyone got it wrong :) Debug or Release? The debug code (bugs in Reflector corrected by looking at the MSIL)

SomeIDisposableClass CS$3$0000;
bool CS$4$0001;
CS$3$0000 = new SomeIDisposableClass();

Label_0007:
try
{
SomeCode();
goto Label_0021;
}
finally
{
Label_0011:
CS$4$0001 = CS$3$0000 == null;
if (CS$4$0001)
{
goto Label_0020;
}
CS$3$0000.Dispose();
Label_0020:;
}
Label_0021:;

And yes, it is silly. It's storing the result of the null-check The Release code

SomeIDisposableClass CS$3$0000;
CS$3$0000 = new SomeIDisposableClass();

Label_0006:
try
{
SomeCode();
goto Label_0017;
}
finally
{
Label_000D:
if (CS$3$0000 == null)
{
goto Label_0016;
}
CS$3$0000.Dispose();
Label_0016:;
}
Label_0017:

edit: the rules for goto-within-try are If the goto statement exits one or more try blocks with associated finally blocks, control is initially transferred to the finally block of the innermost try statement. When and if control reaches the end point of a finally block, control is transferred to the finally block of the next enclosing try statement. This process is repeated until the finally blocks of all intervening try statements have been executed.

Lost User · modified on Monday, June 14, 2010 11:55 AM

d@nish wrote:

Why and when would you write a code like that?

There's even a CodeProject-article[^] to answer that one! :-D

I are Troll :suss:

Al Beback · modified on Monday, June 14, 2010 11:55 AM

d@nish wrote:

As far as its equivalent is concerned, just see the IL through ILDAsm or reflector and it would make things a bit clear.

I know, but shamefully, I'm IL challenged. :)

ShamWow

Lost User

harold aptroot wrote:

Wow, everyone got it wrong Debug or Release?The debug code (bugs in Reflector corrected by looking at the MSIL)

Bugs? +5 :thumbsup:

I are Troll :suss:

Lost User

Bugs like this one.. if ((CS$3$0000 == null) != null) That's not even possible, and the IL for that part is just

L\_0011: ldloc.0 
L\_0012: ldnull 
L\_0013: ceq 
L\_0015: stloc.1 
L\_0016: ldloc.1 
L\_0017: brtrue.s L\_0020

So Mr Reflector just skipped over a load/store and made up a comparison :wtf:

Al Beback

That's what I was looking for, thanks!

ShamWow

dan sh

Nice find. :) From now on, I am going to have this in my windows forms application (of course with proper comments):

public class AppCursor : IDisposable
{

    Cursor \_currentCursor = null;
    bool \_setDefault;

    public AppCursor(Cursor cursor, bool setDefault)
    {
        \_currentCursor = Cursor.Current;
        \_setDefault = setDefault;
        Cursor.Current = cursor;
    }

    #region IDisposable Members

    public void Dispose()
    {
        Cursor.Current = (\_setDefault) ? Cursors.Default : \_currentCursor;
        
        // Even with disposing the cursor object, form works but am not sure whether it should be there or not.
        \_currentCursor.Dispose();
        \_currentCursor = null;
    }

    #endregion
}

Not Active

Chris should put that in the advertising. There is an app article for that. :-D

I know the language. I've read a book. - _Madmatt