Hi Piotr,
Thanks for the links, the confusing code now makes much more sense.
Ahh you gotta love C++...
Robert.
On Sat, Nov 8, 2008 at 7:53 PM, Piotr Rak <[EMAIL PROTECTED]> wrote:
> 2008/11/8 Robert Osfield <[EMAIL PROTECTED]>:
>> Hi Poitr,
>>
>> Why do you use a typedef in this context? Which not just define a
>> operator T* const()?
>>
>> Also the valid() check is redundant.
>>
>> Robert.
>
> Hi Robert,
>
> Please notice that following code doesn't add conversion to T*
> it adds conversion to member pointer of class ref_ptr<T> happends to
> be of type T*.
>
> typedef T* ref_ptr<T>::*unspecified_type_bool;
> //should be read :
> unspecifed_type_bool is name of pointer to member of ref_ptr<T> of type T*.
>
> so type unspecified_type_bool can contain address of any member of
> ref_ptr which is of type T*.
>
> I could be address of any arbitrary member of ref_ptr<> or infact even
> member function pointer.
> if we had member field 'XYZ _dummy'; it could be:
>
> typedef XYZ ref_ptr::*unspecified_type_bool;
>
> I don't want to introduce implicit conversion ref_ptr<T> to T*
>
> so code like:
>
> class T;
> void foo (T*) {}
>
> void bar ()
> {
> ref_ptr<T> ptr;
> foo (ptr); //illegal no conversion to T* from pointer to some member
>
> if (!! ptr) {}// still legal, will call operator! () which is
> redundant infact, but i left it alone for
> OSG_USE_REF_PTR_IMPLICIT_OUTPUT_CONVERSION case
> }
>
> works as it did without OSG_USE_REF_PTR_IMPLICIT_OUTPUT_CONVERSION defined;
>
> but now following becomes legal:
>
> if (ptr) {} // woot !
>
> Check valid() is needed since address of member _ptr is always
> positive for ref_ptr somehere in memory, ofcourse.
>
> Whole technique I used is 'safe bool idiom',
> described in few textbooks (do not remember which, but can check that
> after weekend).
> Describtion online found here (and many other places):
>
> http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Safe_bool
>
> For sure better then I did ;-)
>
> I dont want to use member function pointer like showed there, since it
> is less effective than pointer to member. For more information about
> this issue, please see
> http://lists.boost.org/Archives/boost/2003/09/52856.php
>
> Probably I should have reference to this resources in code before.
> Hope this explains bit, those few lines code I have added :)
>
> Cheers, Piotr
>
>> On Fri, Nov 7, 2008 at 9:35 PM, Piotr Rak <[EMAIL PROTECTED]> wrote:
>>> Hi,
>>>
>>> Attached contains small, yet useful addition:
>>> bool conversion for ref_ptr, when no implicit conversion to T* is used.
>>> Was surprised, it wasn't there already!
>>>
>>> Cheers,
>>> Piotr
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