Re: variadic templates

"Earl Purple" <>
Tue, 22 Aug 2006 09:48:48 CST
"Gene Bushuyev" wrote:

The easy solution to that problem is writing a simple few lines program for
automatically generating code. It will also be easier for a programmer to reason
about the design and to debug it, and it works with not so smart compilers as
well. I have a number of solutions that automatically generate code at the
pre-build stage and that proved to work very well.
I think it's time to standardize the facilities to execute code generators
during compilation, that would make it easily portable to all platforms.


Gene Bushuyev (

I think someone else made a comment about pre-compile recently, i.e.
you write something in a higher-level script which is not C++ and then
auto-generate the appropriate C++. A bit like the way IDL works, I
guess, or yacc for C++.

With my exact situation above, I doubt it would be possible using
variadic templates to produce the related types
ParamBinder<T>::binder_type. It may be made possible to iterate through
the exact parameter types, but I can't see it extending to related
types (even if they can be template-typedefed so it might be
ParamBinder<T> instead of the extra binder_type). It would be possible
to modify my model by not using lazy construction, i.e .calling
bindParams and createObject in one go.

I would like to see variadic templates for straightforward factories
though. Such a factory could look something like:

template < typename T, typename BASE, typename ...Var >
class Factory< T > : public FactoryBase< BASE >
   Var args;

   explicit Factory( Var va ) : args( va ) {}

   T* create() const
         return new T( args );

args and va above would be expanded into the fully-typed argument list.
You would also probably want to write a function to create that
factory, so you'd want variadic arguments to template functions too. If
X is a type that derives from Y and takes a constructor X( int,
std::string ) then you'd invoke the function

make_factory< X, Y >( 25, std::string("foo") );

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