Does this make sense ?
Having a simple class
class Test { public Test() { // Do whatever } } and then instantiating it
using(new Test()) { // Nothing in here } The using statement is there just to make sure Test is disposed. When will it be disposed if I just call
new Test() Test isn't IDisposable, so that won't even compile. But if it was disposable, yes using will do it, and new by itself won't. It is an unusual usage, but I've seen similar. Rarely.
Based on your comment (main question), I suspect that you are confusing garbage collection and disposal. There is no way to forcibly make something get collected, short of GC (which you should not do). Unless you have a really good reason to want it collected, just let it be - chances are it is "generation 0" and will be collected cheaply anyway.
Also, the "do whatever" suggests doing something in a constructor but not caring about the created object; a static method would be preferable:
public class Test { /* could be static */ public static void DoSomething() { ... } } ... Test.DoSomething(); 
HtmlWriter.RenderBeginTag(), RenderEndTag(). If you throw exception between these two (or otherwise forget to RenderEndTag), it results in malformed html/xml. So, I wrote extension method over RenderBeginTag, which returns IDisposable class simply calling RenderEndTag, and I now clearly see, (via indentation) where is tag opened/closed. Another examples is measuring of how long did some block take to run. But, YMMV.
By not assigning the instance to a variable, it will be eligible for GC as soon as it goes out of scope.
Or, is there something else you are trying to accomplish with this?
Recommended reading:
TestimplementsIDisposable?