Re: polymorphism on template parameters

From:

Pete Becker <pete@versatilecoding.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 5 Aug 2008 09:42:27 -0400

Message-ID:

<2008080509422716807-pete@versatilecodingcom>

On 2008-08-05 08:46:12 -0400, Renato Golin <rengolin@gmail.com> said:

class Stone : public Thing <NoMove, NoEat, NoReproduce>
{
public:
     Stone() { }
     ~Stone() { }
};

int
main () {
     Thing<>* s = new Stone();
     return 0;
}

First, when things start getting tangled, reduce the number of template
arguments. That makes it easier to see what's going on. After you've
figured things out, add the rest of the details back in.

I get the error:

In function ???int main()??":
error: cannot convert ???Stone*??" to ???Thing<MovePolicy, EatPolicy,
ReproducePolicy>*??" in initialization

Thing<MovePolicy etc.> and Thing<NoMove etc.> are two unrelated types.
The same problem occurs in this code:

class Base1 { };
class Base2 { };
class Derived : public Base1 { };
Base2 *ptr = new Derived; // error: no conversion from Derived* to Base2*

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)