Re: Pure virtual destructor in template class

From:

Pete Becker <pete@versatilecoding.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 18 Nov 2008 11:52:45 -0500

Message-ID:

<2008111811524575249-pete@versatilecodingcom>

On 2008-11-18 11:33:49 -0500, Tonni Tielens <tonnitielens@gmail.com> said:

I'm trying to create a pure virtual class describing an interface.

There's no such thing as a pure virtual class. The term you're looking
for is abstract class.

Normally, when I do this I make the destructor pure virtual so that,
even if there are no members in the class, it cannot be instantiated.

The difference now is that I'm making a generic interface with
template arguments. Template classes should be defined in the header
file, but it is not allowed for a destructor's definition to be in the
class definition if the destructor is pure virtual. Atleast not with
GCC -pedantic and I understand this is correct behavior. I'm unsure on
how to solve this. I know I don't really have to put a pure virtual
destructor in the class, but I think it's good practice so if it's
possible I would like to stick to this.

My code looks like the following:

template <typename TypeA, typename TypeB>
struct MyInterface
{
virtual ~MyInterface() = 0;

virtual void Foo(TypeA a, TypeB b) = 0;
};

I already found that I can resolve the compilation errors, by adding

template <typename TypeA, typename TypeB>
MyInterface<TypeA, TypeB>::~MyInterface() {}

in the same file after the class definition, but I'm not sure if this
is the common way to do this.

It is.

Is there a correct way to do this or
should I leave the pure virtual destructor out?

You can't leave the destructor out. Try it.

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