Using statement in C# without implementing Dispose Method

Question

I am trying to understand using block in C#. Can I create a custom object inside Using statement like the below which doesn't implement the IDisposable interface?

Class A
{
}

using(A a = new A())
{
}

It gives me error saying "Error 1 'ConsoleApplication1.A': type used in a using statement must be implicitly convertible to 'System.IDisposable'"

How to correct this error? I do not want to do Class A : IDisposable

Any other way? Or it is a mandatory requirement that we need to implement IDisposable Dispose method in these kind of custom objects which we use inside using block?

EDIT: I am NOT expecting the definition that is there in the MSDN and thousands of websites. I am just trying to understand this error and also the rectification

Could you elaborate on why you don't want to use IDisposable? Maybe something better could be found. — antiduh
– antiduh, Commented Dec 5, 2013 at 6:19
@antiduh: Well let me rephrase my words for you. What is the meaning of that error "Convertible" — Jasmine
– Jasmine, Commented Dec 5, 2013 at 7:43

Pavel Nikolov · Accepted Answer · 2013-12-05 06:03:16Z

12

Using blocks are syntactic sugar and only work for IDisposable objects.

The following using statement:

using (A a = new A()) {
// do stuff
}

is syntactic sugar for:

A a = null;

try {
  a = new A();
  // do stuff
} 
finally {
  if (!Object.ReferenceEquals(null, a))  
    a.Dispose();
}

edited Dec 5, 2013 at 6:03

Pavel Nikolov

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answered Dec 5, 2013 at 5:56

syazdani

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7 Comments

Jonas Høgh Over a year ago

Why 2 calls to new A?

Pavel Nikolov Over a year ago

You should just leave a = new A(); since variable a already exists

syazdani Over a year ago

whoops, you are right.. and it seems to have been fixed up by some editors (thank you!)

Jasmine Over a year ago

@syazdani: This I know 3 years back and my question is not that. My question is completely different from what you have understood

syazdani Over a year ago

All "implied convertible" means is that the runtime should be able to cast a given object to a given type and get a meaningful result (in this case, casting A to IDisposable). In some situations, the compiler can check for this during compile time and give you an error if it is not possible (as it is doing for you because A does not implement IDisposable). Read more here: en.wikipedia.org/wiki/Type_conversion

|

Jonas Høgh · Accepted Answer · 2013-12-05 05:55:40Z

4

The whole point of using is to create the equivalent of a try block with a call to Dispose in finally. If there is no Dispose method, there is no point to the using statement.

answered Dec 5, 2013 at 5:55

Jonas Høgh

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