Re: Correct use of templated class'es inner structs/classes?

[Rob Williscroft]

Tomas Ukkonen wrote in pan.2004.05.07.09.54.54.797578@iki.fi">news:pan.2004.05.07.09.54.54.797578@iki.fi in 
comp.lang.c++:

> Hi
> 
> I'm currently trying to make my old code to compile with 
> new gcc 3.4.0. It compiles correctly in 3.3.3 so I'm not
> sure if this is compiler bug or not.
> 
> 
> Code very close to a example below fails to compile
> because gcc 3.4.0 complains:
> "error:   expected a type got 'Y<T>::particle'"
> at Y<T>::func()'s iterator declaration.
> 
> 
> EXAMPLE
> (I actually haven't tried to get this compile).

Why not ?.

> -----------------------------------
> 
> example.h:
>   template <typename T>
>   class Y{
>     public:
>     
>     struct particle {
>       OtherClass<T> data;

                T data; // to make a compilable example !

>     };
> 
>     void func();
>     
>     std::vector<Y<T>::particle> list;

        std::vector< typename Y<T>::particle > list;

However Y (without the <T>) is an injected class name so you should
be able to do this:

        std::vector< Y::particle > list;

However of the compilers I tried on CBuilderX previeiw (EDG based)
handled it, g++ 3.4 (prereleas) didn't, your version maybe later than 
mine so try it.


>   }

missing ;

> 
> 
> example.cpp:

This should be in a header file.

>   template <typename T>
>   void Y<T>::func(){
>     typename std::vector< Y<T>::particle >::iterator i;

     typename std::vector< typename Y<T>::particle >::iterator i;


>     
>     i = list.begin();
>     
>     while(i != list.end()){
>       // do something
>     }
>   }

missing ;


The typename is required as Y<T> is dependant on a template argument
so particle in Y<T>::particle is a dependant-name, you need to tell
the compiler its a type, otherwise it assumes its a non-type.

g++ 3.3.x didn't require this as it didn't support 2-phase name
lookup, as its supposed to. i.e. 3.4 is correct.

HTH.

Rob.
-- 
http://www.victim-prime.dsl.pipex.com/