How to convert a try-catch-finally block to using statement in c#?

Question

Say we create a IDisposable object, and we have a try-catch-finally block

var disposable= CreateIDisposable();
try{
  // do something with the disposable.
}catch(Exception e){
  // do something with the exception
}finally{
  disposable.Dispose();
}

How do I convert this to a using block?

If it were

var disposable= CreateIDisposable();
try{
  // do something with the disposable.
}finally{
  disposable.Dispose();
}

I would convert to

using(var disposable= CreateIDisposable()){
     // do something with the disposable.
}

How would I do this with the catch block?

try{
  using(var disposable= CreateIDisposable()){
     // do something with the disposable.
   }
}catch(Exception e){
  // do something with the exception
}

You have two choices, either using the code that you show (with the using statement inside the try clause, or with the entire try / catch within the using block. If no exception is thrown, then the code is nearly identical (the Dispose` call happens at the end, though the underlying assembly code will look different). If there is an exception, then, in either case, the catch clause would execute first and then the Dispose call on the way out the door. I'd call it a toss-up. Of course, your try / catch/ finally code is perfectly good as well — Flydog57
– Flydog57, Commented Feb 24, 2020 at 23:52

madreflection · Accepted Answer · 2020-02-24 23:50:31Z

3

You're close. It's the other way around.

In reality, the CLR doesn't have try/catch/finally. It has try/catch, try/finally, and try/filter (that's what it does when the when clause is used on catch). try/catch/finally in C# is just a try/catch within the try block of a try/finally.

So if you expand that and convert the try/finally to using, you get this:

using (var disposable = CreateIDisposable())
{
    try
    {
        // do something with the disposable.
    }
    catch (Exception e)
    {
        // do something with the exception
    }
}

answered Feb 24, 2020 at 23:50

madreflection

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2 Comments

Flydog57 Over a year ago

@KristjanKica: I ran out of room in my comment on your question. But, I was going to say that this is the way I normally write these (though I have done try / catch / finally before

kkica Over a year ago

that makes more sense. My code would exceute "finally" before "catch"

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