Re: [boost] Named Template Parameters

From: David A. Greene (greened_at_[hidden])
Date: 2002-08-07 15:30:46

Paul Mensonides wrote:

> There are several ways to maintain an interface while changing arities.
> 
> template<int> struct some_class;
> 
> template<> struct some_class<1> {
>     template<class T> struct args {
>         // ...
>     };
> };
> 
> template<> struct some_class<2> {
>     template<class T, class U> struct args {
>         // ...
>     };
> };

Erk...this strikes me as a bit ugly.  Doesn't the interface for
some_class have to be re-declared in each specialization?
I don't see how this provides any decoupling.  I'm missing
something important here.

> You can also extract parameter types from a function type, etc..

I don't follow you here.

>>In any event, I've seen calls in various places (c.l.c++.m
>>and here, I think) for variable-length template parameter
>>lists.  What are those good for?  Typelists seem to provide
>>the same functionality.  Well, in the same way std::vector
>>provides variable-length function argument lists.  :)
> 
> Typelists only supply the same functionality for types.  They don't extend to
> other variable-length arities such as parameter lists.

Sure.  I guess I don't understand how variable-length template
parameter lists would be used, then.  I'm missing a piece of
the puzzle.

                      -Dave

-- 
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