Re: Making a smart pointer which works with incomplete types
On Sep 7, 4:11 pm, "Alf P. Steinbach" <al...@start.no> wrote:
* Kai-Uwe Bux:
Alf P. Steinbach wrote:
* Kai-Uwe Bux:
Alf P. Steinbach wrote:
* Juha Nieminen:
Then it occurred to me: Is there any reason this pointer cannot b=
e
static? Like this:
//-----------------------------------------------------------------=
-
template<typename Data_t>
class SmartPointer
{
...
static void(*deleterFunc)(Data_t*);
...
public:
SmartPointer(Data_t* d): data(d)
{
deleterFunc = &deleter;
}
...
};
template<typename Data_t>
void(*SmartPointer<Data_t>::deleterFunc)(Data_t*) = 0;
//-----------------------------------------------------------------=
-
This way the pointer to the deleter will be stored in the program
only
once, and most importantly it will not increment the size of the sm=
art
pointer.
This feels so glaringly obvious to me now that I really wonder wh=
y
this wasn't suggested to me to begin with. Is there some error here=
I'm
missing?
Yeah. Successive smart pointer instantiations can change the common
deleter func pointer.
[snip]
How?
Sorry, I reacted to the static pointer. As I wrote use a template
parameter instead. The only valid reason for having a pointer to that
function is to change the pointer, and that's apparently done in the
constructor body,
Really? Then a smart pointer working with incomplete types
(in the sense above) either does not qualify as a valid
reason or there must be a way without that (static) pointer.
Which is it? and if it is the second, which way of making a
smart pointer work with incomplete types do you have in
mind?
Consider the following:
template< typename T >
void destroy( T* );
template< typename T >
class SmartPointer
{
...
public:
~SmartPointer() { if( ... ) { destroy( myReferent ); } }
};
It achieves the same as the original code without any static pointer.
No. With the original code, you can delete the pointer in a
context where the type is incomplete. with your code, you
can't.
For more flexibility (in the direction that a static pointer
could add flexibility) make the deleter a template parameter.
Which would require the type to be complete when you
instantiation the template.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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