Boost logo

Boost :

From: Mat Marcus (mmarcus_at_[hidden])
Date: 2000-10-02 05:46:20

At 7:55 AM -0400 10/1/00, John Maddock wrote:
>Thanks to a slew of recent posts here and elsewhere regarding VC6 template
>workarounds, I've been able to get most of the type_traits library and
>hence call_traits working with VC6, in particular you can now use
>call_traits on VC6 to solve the "reference to reference" problem.

Great work. We'd been meaning to leverage our "simulated partial
specialization" techniques to update type_traits and call_traits to
work on VC6. Of course our employer has already cut us a fair amount
of slack in developing and posting the initial idea, so it may taken
us some time. We also hadn't solved the is_ref problem until David
Abrahams recent post suggesting that the problem could be reduced to
is_const. Anyway I'm glad to see you make use of our work. I have
also learned some new techniques from you. The way you reduce of
is_ref to is_const is quite elegant. I also like the trailing *const
volatile qualifiers on your is_pointer discriminator, and the static
T members instead of the (T*)0 casting tricks.

A couple of suggestions:

1) You probably will want to retain something like the PointerShim class below

At 3:03 PM -0700 9/29/00, Mat Marcus wrote:
> struct PointerShim {
> // Since the compiler only allows at most one non-trivial
> // implicit conversion we can make use of a shim class to
> // be sure that IsPtr below doesn't accept classes with
> // implicit pointer conversion operators
> PointerShim(const volatile void*); // no implementation
> };
> // These are the discriminating functions
> char IsPtr(PointerShim); // no implementation is required
> int IsPtr(...); // no implementation is required

Otherwise classes with implicit conversions to pointer types (bad
style of course) will confuse is_ptr.
Perhaps the test suite should include something like :

struct IntegerSmartPtr{
        operator int*(); // try to confuse is_ptr

2) Right now is_same<int, int&>, is_ptr<int*&> return true. This
seems undesirable. Perhaps you might make use of the is_reference
metafunction in the implementations of the misbehaving metafunctions.
Of course the test suite could be augmented too.

- Mat

BTW, is anyone from this list going to attend the Generative
Programming/C++ conference in Erfurt, Germany next week?

Boost list run by bdawes at, gregod at, cpdaniel at, john at