When creating an element that implements IDisposable, Dispose() is called at the end of the using block also if an exception is thrown, if I'm correct.
However, when creating a new element of ClassB within the constructor of a disposable element, will the object of ClassB also be disposed if IDisposable is implemented?
using (ClassA a = new ClassA(new ClassB())) { } This may apply to classes that are related to Stream. However, does this apply in general?
ClassB would only be disposed if the dispose method of ClassA calls dispose on it.
class ClassA : IDisposable { private ClassB b; public ClassA (ClassB b) { this.b = b; } public void Dispose() { this.b.Dispose(); } } If it doesn't you'll need to dispose of it separately:
using (ClassB b = new ClassB()) using (ClassA a = new ClassA(b)) { } 
ClassA constructor would result in leaking the ClassB instance.
ClassB object is shared among many ClassA instances?
ClassA did dispose of ClassB, if you used the second example it shouldn't cause a problemShort answer, no. If ClassB implements IDisposable, you should wrap it in a using block too:
using (var b = new ClassB()) using (var a = new ClassA(b)) { // do stuff } Keep in mind that everything you pass to a constructor, or any other method which accepts parameters is evaluated before the constructor or method is invoked.
Some classes, like StreamWriter does with a Stream, will dispose whatever is passed through the constructor, but it's common to leave the disposing to whoever actually instantiated the object.
