Thread: my code breaks unique pointer rule?

I'm no expert on Microsoft extensions but I suspect, in this case, the unique keyword is an attribute of the pointer passed by the caller (i.e. main()), not to whatever the function might do to the argument.

In other words, the function is allowed to assume the pointers passed to it are "unique".

Thanks CornedBee,


When I add [unqiue] to Foo class, compile not pass and compile error is,

1>d:\visual studio 2008\projects\test_uniquepointer1\test_uniquepoint er1\main.cpp(12) : error C3115: 'unique': this attribute is not allowed on 'ptr1'
1> d:\visual studio 2008\projects\test_uniquepointer1\test_uniquepoint er1\predefined c++ attributes (compiler internal)(1155) : see declaration of 'unique'
1> attribute can only be applied to: 'member', 'interface member function', 'formal argument of interface member function', 'typedef'

if you think we can make the pointer unique by adding the unique attribute to the foo method of class Foo, could you show me how to solve the compiler error please? :-)

Originally Posted by CornedBee

That's one part of it.

The second part is that the attribute might not be inherited. It could be part of the co-variance principle (overriding methods may be more lax in what they accept - note that this is a principle from type theory, NOT C++), or it could simply be an implementation issue.

Or the attribute could simply be not enforced. Do you know if the compiler actually uses flow analysis to enforce the attribute?

Good point, Mats!


Do you have any suppor documents from MSDN or? :-)

Originally Posted by matsp

I have a felling the compiler doesn't actually CHECK the unique-ness of the pointer [for more complex cases it would be impossible to know anyways], but it's more like a contract - you promise to follow your part of the contract, and if you don't the "penalty clause" gets enforced, e.g. the behaviour of the called function is undefined.

--
Mats

Thanks grumpy,

Originally Posted by grumpy

In other words, the function is allowed to assume the pointers passed to it are "unique".

How do you prove that?


regards,
George