Is it safe to create and use a disposable object inline?

Question

I have seen so many times developers using a disposable object inline, here for instance. By inline I mean:

var result = new DataTable().Compute("1 + 4 * 7", null);

I know that the Dispose method won't be called, but since no reference is held to the object, how will the garbage collector handle it? Is it safe to use a disposable object like that?

I used a DataTable in my example because it is the only concrete example I found, but my question applies to disposable objects in general. I do not personally use them like that, I just wanted to know if they are handled diffently by the GC if they are used that way.

Answer 1

The key problem here is the timing when Dispose is called, which is just unknown in your example (providing a good implementation of IDisposable — see below). I'd consider using an IDisposable instance without a using statement a code smell. The class is implementing IDisposable for a reason, and thus you as a user should obey its contract.

However, note that in a correct implementation of IDisposable the class'es finalizer handles the disposal of an un-disposed object. Hence even if not instantiated within a using, the disposal shall be performed, but in unknown time and on a different (the GC's) thread.

I just wanted to know if they are handled diffently by the GC if they are used that way.

No, the GC treats all object alike and doesn't treat IDisposable implementations anyhow differently. However, in a correct implemenetation of IDisposable the Finalize method (invoked by the GC on every object unless suppressed on a per-object basis) call would lead to invoking the Dispose.