Andre Poenitz <[EMAIL PROTECTED]> writes:
>> John Levon <[EMAIL PROTECTED]> writes:
>>
>> | I much prefer Andre's way. Compare
>> |
>> | InsetSomething * i = inset->asSomethingInset();
>> | if (!i)
>> | break;
>> |
>> | with
>> |
>> | if (inset->lyxCode() == SOMETHING_CODE) {
>> | InsetSomething * i = static_cast<InsetSomething*>(i);
>> | ...
>> | }
>> |
>> | Does anyone have a problem with this form of RTTI ?
>>
>> What about some:
>>
>> class Inset {
>> public:
>> template <typename T>
>> T * insetAsType() {
>> return static_cast<T*>(this);
>> }
>> };
>>
>> Which in the usual case would not be implemented with static_cast as
>> above, but rather with some dynamic_cast or explit type checking with
>> some rtti.
>
| But if it is implemented with rtti, we could use rtti properly, couldn't we?
| And static_cast<> does not solve the problem.
agree static_cast is not a solution at all.
we want to disallow crosscast and only allow upcast.
Inset
/\
/ \
/ \
AInset BInset
Inset * i = new BInset;
Ainset * a = dynamic_cast<AInset*>(i);
a should now be 0. But is that true it is further checking
needed?
It seems that I am right... it works as wanted:
#include <iostream>
using namespace std;
class Inset {
public:
virtual ~Inset() {}
};
class AInset : public Inset {};
class BInset : public Inset {};
int main()
{
Inset * i = new BInset;
AInset * a = dynamic_cast<AInset*>(i);
BInset * b = dynamic_cast<BInset*>(i);
cout << a << endl << b << endl;
}
./upcast
0
0x8049e40
So.. then does this work as well:
class Inset {
...
template <typename T>
T * asType() {
return dynamic_cast<T>(this);
}
};
This seems to work:
#include <iostream>
using namespace std;
class Inset {
public:
virtual ~Inset() {}
template <typename T>
T asType() {
return dynamic_cast<T>(this);
}
};
class AInset : public Inset {};
class BInset : public Inset {};
int main()
{
Inset * i = new BInset;
AInset * a1 = dynamic_cast<AInset*>(i);
BInset * b1 = dynamic_cast<BInset*>(i);
AInset * a2 = i->asType<AInset*>();
BInset * b2 = i->asType<BInset*>();
cout << a1 << endl << b1 << endl;
cout << a2 << endl << b2 << endl;
}
./upcast
0
0x8049f18
0
0x8049f18
_but_ I guess a lot of complier have problems with RTTI...
--
Lgb
