Re: [Boost-users] [mpl] Is it possible to mpl_assert depending on the derivation of a class

From: Hughes, James (jhughes_at_[hidden])
Date: 2007-08-21 06:24:34

> Hughes, James wrote:
> > Hello all,
> >
> > I want some template code to assert if the passed in 
> template type is 
> > NOT derived from a particular base class.
> >
> > I've looked through the Template Metaprogamming book, but 
> haven't seen 
> > anything that can do this, but I seem to remember something along 
> > those lines.
> >
> > Can anyone help?
> >
> > James
> >
> >   
> Hi James,
> 
> the easiest way is something like the following:
> 
> #include <boost/type_traits.hpp>
> #include <boost/static_assert.hpp>
> 
> BOOST_STATIC_ASSERT (boost::is_base_of<Base, Derived>::value);
> 
> Hope this helps,
> 
> Martin

Thanks Martin - I knew I had seen it somewhere.

That covers the first point, but I've just realised I need to be a bit
cleverer. The incoming type can either be the type itself or a pointer
to the type, or a boost::shared_ptr to the type, and the type must be
derived as the original question. Depending on which it is I need to do
slightly different things, so I need to, effectively, conditionally
compile a bit of code depending on the results of the tests, or assert
if the type (after getting rid of the pointer/shared point bit) isn't
derived from my base class.

Basically I'm iterating through a vector of the incoming type and
calling a function in the type stored. That function comes from the base
class, but in order to be really generic I need to handle the shared_ptr
and pointer cases.

I think I need mpl for that, but I only get to chapter three of the book
before my head starts to hurt. Any ideas/hints/places I can look?

James

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