Where to not use IDisposable implementation?

Question

My question is specific to, why and where not to implement IDisposable interface.

If I am not using & consuming any unmanaged resources, still is it good practice to implement IDisposable interface.

What are the advantages or disadvantages if I do it? or is it good practice to implement it?

Please advise.

Answer 1

You implement IDisposable for one of two reasons:

1. If you have Unmanaged resources to free.
   You do this because this is the only way for the GC to know how to free unmanaged resources which otherwise it doesnt know about. This is about WHAT resources to free. This case is actually quite rare - more often than not you access unmanaged resources through existing managed objects. This case requires a full "official recommended" implementation. Generally you should wrap unmanaged resources in their own separate (managed) class that does the IDisposable implimentation (rather than including unmanaged resources in other larger objects).

2. If your class contains objects that impliment IDisposable.
   You do this not because the objects won't get free if you don't (they will) but because you want to be able to control WHEN those resources are freed. Having a dispose impliementation that disposes disposable members of a class means that consumer can apply a using statement to easily control WHEN resources are freed. In pratice more often than not this is the main reason for implementing IDisposable. Note that if your class is sealed you can get away with a mimimal IDisposable implementation here - I.e just Dispose - there is no need for the full blown "official recommended' implimenation.

It follows that if neither of these cases applies then no need to implement.

Answer 2

If a class implements IDisposable, that will generally impart to any code which creates instances of that class a responsibility to ensure that Dispose gets called on that instance before it is abandoned; it may fulfill this responsibility either by calling Dispose on the object itself when it is no longer needed, or by making sure that some other object that receives a reference accepts "ownership" and responsibility for it. In the majority of cases, when code is written correctly, each IDisposable object upon which Dispose has not yet been called, will at every point in time, have exactly one other entity (object or execution scope) which "owns" it. During the lifetime of the IDisposable object, ownership may get passed among different entities, but when one object receives ownership the former object should relinquish it.

In many cases, objects will be used in such a fashion that tracking ownership is not difficult. Generally, any object whose state is ever going to be modified should have exactly one owner and that owner will know when the object is no longer needed. Additionally, because modification of the owned object's state would constitute modification of the owner's state, the owner itself should have a single owner. In such cases, requiring the owner to call Dispose will not pose any difficulty (the owner's owner should call Dispose on it). There is, however, a 'gotcha' with this principle: it's possible for an object to create an instance of a mutable class but never mutate it nor allow anyone else to do so. If the mutable class in question simply holds values and does not implement IDisposable, objects which hold references to the things that will never actually mutate need not concern themselves with ownership. This can allow some major simplifications, since it will be possible for many objects to hold references to the non-changing object and not have to worry about which of them will use it last. If, however, the mutable class in question implements IDisposable, such simplifications are no longer possible.