Re: Compilation problem with templates

From:

Jerome Durand <aNOSPAMaj.durand@def2shoot.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 26 Apr 2007 17:59:39 +0200

Message-ID:

<f0qguo$gfq$1@reader1.imaginet.fr>

mlimber a ?crit :

On Apr 26, 7:23 am, Jerome Durand <j.dur...@def2shoot.com> wrote:

I'm trying to write something along the following lines
but I cannot get this to compile.

        template <typename derived> struct Base {
                typedef typename derived::valueType valueType;
                virtual valueType Value() = 0;
        };

        struct CharValue: Base<CharValue>{
                typedef char valueType ;
                valueType Value() {return 'a';}

        };

        struct IntValue: Base<IntValue> {
                typedef int valueType ;
                valueType Value() {return 1234;}
        };

The compiler outputs (first error only):
Error 1: 'valueType' : is not a member of CharValue'

Could someone tell me what is wrong with this?

You're effectively trying to use CharValue and IntValue before they're
defined. Why not simplify it like this:

        template <typename T> struct Base {
                typedef T valueType;
                virtual valueType Value() = 0;
        };

        struct CharValue: Base<char>{
                valueType Value() {return 'a';}

        };

        struct IntValue: Base<int> {
                valueType Value() {return 1234;}
        };

Cheers! --M

because this is a trimmed down version of my problem,
where there's more than a single function and hence
more than a single return type required.

-J-