Question

The following doesn’t work:

    public string foo()
    {
        using (Random myRandomChoice = new Random())
        {
            return myRandomChoice.Next(10).ToString();
        }
    }

The following is errors:

    public string foo()
    {
        Random myRandomChoice = new Random();
        return myRandomChoice.Next(10).ToString();
    }

The error message for the first foo is concerning Random not being implicitly convertable to System.IDisposable.

Is this a deliberate ploy withing the syntax of the language so you only use using in specific circumstances e.g when dealing with database connections? or can I explicitly convert Random to type IDisposable so that the initial foo works?

Is there a list available of types that would be better declared with using ?

Answer 1

A using statement is a way to guarantee that Dispose is called on an object even when an exception is thrown. It is therefore meaningless when the object does not implement IDisposable.

The following code examples are equivalent:

(1) A using statement:

using (MyClass myObj = new MyClass())
{
    ...
}

(2) Disposing in a finally block:

try
{
    MyClass myObj = new MyClass();
    ...
}
finally
{
    myObj.Dispose();
}

As you can see, all the using statement achieves is disposal of the object, therefore it makes no sense if you object doesn’t implement IDisposable.

FXCop has a rule for checking that you have used using statements for your IDisposable types. See this StackOverflow question for other ways to find which types implement IDisposable and can be used in a using statement.

See the MSDN documentation for more information.