Geoff Fortytwo wrote:
>> Is it legal to do partial explicit instantiation?
>> [...]
>>
>> typedef StandardCreator<Column, TheProduct>
>>     StandardColumnCreator<TheProduct>;

Christopher Eltschka wrote:
>> You cannot make a template typedef - a typedef *must* denote
>> a single type.

James Kuyper wrote:
> However, you can achieve much the same effect as a template typedef,
> by defining a typedef member of a templated class:
>
> template<TheProduct> class StandardColumn {
>     typedef StandardCreator<Column, TheProduct>  Creator;
> };
>
> Then you use StandardColumn<T>::Creator instead of
> StandardColumnCreator<T>.

Here's a question for the committee:
Why are template typedefs not allowed (simply an oversite)?

Another related question: Does the method above work in all cases,
i.e., is it a general substitute for all template typedefs?
(If so, then that probably answers my first question.)

-- David R. Tribble, dtribble@technologist.com --


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Geoff Fortytwo wrote:
>
> Is it legal to do partial explicit instantiation?  And if so, am I doing
> it correctly?  MSVC++ 5.0 doesn't like the last 2 lines of the following
> code (I'm trying to implement a generic Factory Method pattern):
>

[...]

> typedef StandardCreator<Column,TheProduct>
> StandardColumnCreator<TheProduct>;

You cannot make a template typedef - a typedef *must* denote
a single type.


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Christopher Eltschka wrote:
>
> Geoff Fortytwo wrote:
> >
> > Is it legal to do partial explicit instantiation?  And if so, am I doing
> > it correctly?  MSVC++ 5.0 doesn't like the last 2 lines of the following
> > code (I'm trying to implement a generic Factory Method pattern):
> >
>
> [...]
>
> > typedef StandardCreator<Column,TheProduct>
> > StandardColumnCreator<TheProduct>;
>
> You cannot make a template typedef - a typedef *must* denote
> a single type.

However, you can achieve much the same effect as a template typedef, by
definine a typedef member of a templated class:

template<TheProduct> class StandardColumn{
 typedef StandardCreator<Column,TheProduct> Creator;
};

Then you use StandardColumn<T>::Creator instead of
StandardColumnCreator<T>.

(I chose class and member names to maximize similarity; other names
might be more appropriate.)


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Christopher Eltschka wrote:
>
> Geoff Fortytwo wrote:
> >
> > Is it legal to do partial explicit instantiation?  And if so, am I doing
> > it correctly?  MSVC++ 5.0 doesn't like the last 2 lines of the following
> > code (I'm trying to implement a generic Factory Method pattern):
> >
>
> [...]
>
> > typedef StandardCreator<Column,TheProduct>
> > StandardColumnCreator<TheProduct>;
>
> You cannot make a template typedef - a typedef *must* denote
> a single type.

However, you can achieve much the same effect as a template typedef, by
definine a typedef member of a templated class:

template<TheProduct> class StandardColumn{
 typedef StandardCreator<Column,TheProduct> Creator;
};

Then you use StandardColumn<T>::Creator instead of
StandardColumnCreator<T>.

(I chose class and member names to maximize similarity; other names
might be more appropriate.)
---
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Is it legal to do partial explicit instantiation?  And if so, am I doing
it correctly?  MSVC++ 5.0 doesn't like the last 2 lines of the following
code (I'm trying to implement a generic Factory Method pattern):


template<typename ProductTypeBase>
class Creator
{
public:
    virtual ProductTypeBase* Create() = 0;
};

template<typename ProductTypeBase, typename TheProduct>
class StandardCreator : public Creator<ProductTypeBase>
{
public:
    virtual ProductTypeBase* Create()  {return new TheProduct;}
};

// This explicit instantiation and typedef compiles fine.
template<> Creator<Column>;
typedef Creator<Column> ColumnCreator;

// But this partial explicit instantiation and typedef don't work.
template<typename TheProduct> StandardCreator<Column,TheProduct>;
typedef StandardCreator<Column,TheProduct>
StandardColumnCreator<TheProduct>;





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Geoff Fortytwo wrote in message <6qp8hc$9p4$1@scnews.sc.intel.com>...
>
>Is it legal to do partial explicit instantiation?  And if so, am I doing
>it correctly?  MSVC++ 5.0 doesn't like the last 2 lines of the following
>code (I'm trying to implement a generic Factory Method pattern):

It's legal in C++, but MSVC++ 5.0 (and 6.0) does not support such a feature.
Sorry.

--
Alberto Barbati
albbarb@tin.it





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