Newbie initial comments on D language - destructor usage

[Edward Diener]

I have a small nit having to do with a general comment which perhaps I
did not really understand. In the documentation on class destructors I read:

"When the garbage collector calls a destructor for an object of a class
that has members that are references to garbage collected objects, those
references are no longer valid. This means that destructors cannot
reference sub objects. This rule does not apply to auto objects or
objects deleted with the DeleteExpression."

This comment makes perfect sense up to the last sentence. Except for a
'scope' class a destructor can not possibly know how it is being called
so if someone can explain to me how a destructor can know when it is OK
to reference sub-objects or not, I would love to hear about it. I would
have thought that referencing sub-objects in a destructor was just
forbidden unless the class was a 'scope' class and had to reference a
sub-object to possibly release a non-memory resource. But perhaps I am
missing the full meaning of the comment and someone can explicate the
issues involved for me.