| Topic: |
DEVELOP > c-Plus-Plus |
| User: |
"verec" |
| Date: |
25 Jun 2005 10:55:32 AM |
| Object: |
template struct polymorphic : public T ??? |
Last week I asked here how I could detect that a T was polymorphic, and
received
very thoughtful and useful replies that I used straight away. Thanks to all who
answered.
This week, it turns out that detecting whether T is polymorphic clashes with
a new requirement, that T be allowed to not be complete.
Last week, this code used to compile:
typedef std::queue<Request> RequestQueue ;
typedef envelope<RequestQueue> Queue ;
This week, I now have to wrap std::queue into a polymorphic
container, as in:
struct RequestQueue : public std::queue<Request> {
// envelope does NOT work with monomorphic types
virtual ~RequestQueue() {} ;
} ;
typedef envelope<RequestQueue> Queue ;
Obviously, I'd like to create some kind of adaptor template ...
template <typename T> struct polymorphic : public T {
virtual ~polymorhic() {}
} ;
intended usage:
typedef polymorphic<std::queue<int> > Queue ;
But this doesn't compile!
The FAQ#35 seems mute here, and I'm beginning to suspect that
something is wrong with my syntax. I also checked
http://www.boost.org/libs/utility/call_traits.htm &
http://www.boost.org/libs/conversion/cast.htm (because it
contained the word: polymorphic_cast, but this turned out
a red-herring)
What would be the correct way to do this?
Many thanks, again.
--
JFB
.
|
|
| User: "verec" |
|
| Title: Re: template struct polymorphic : public T ??? |
25 Jun 2005 07:00:51 PM |
|
|
On 2005-06-25 16:55:32 +0100, verec <verec@mac.com> said:
struct RequestQueue : public std::queue<Request> {
// envelope does NOT work with monomorphic types
virtual ~RequestQueue() {} ;
} ;
typedef envelope<RequestQueue> Queue ;
Obviously, I'd like to create some kind of adaptor template ...
template <typename T> struct polymorphic : public T {
virtual ~polymorhic() {}
} ;
I'm not sure exactly what went wrong, but this first version
was correct ...
#include <iostream>
#include <string>
#include <queue>
template <typename T> struct polymorphic : public T {
virtual ~polymorphic() {}
} ;
void
test_00001() {
typedef polymorphic<std::queue<int> > IntQueue ;
IntQueue queue ;
queue.push(5) ;
queue.push(6) ;
queue.push(7) ;
queue.push(8) ;
while(!queue.empty()) {
int i = queue.front() ;
queue.pop() ;
std::cout << "Just popped: " << i << std::endl ;
}
}
Though I couldn't find a single example of use that particular
syntax (which kind of turns templates inside out) it is
accepted by gcc 4.
--
JFB
.
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