At Mon, 27 Sep 2010 18:22:41 -0700, Steven Watanabe wrote:
AMDG
On 9/27/2010 6:06 PM, Eric Niebler wrote:
I think so far I have failed to make my use case sufficiently clear, so I'll simplify and try to follow the Process. Take the following simple algorithm sum_ints:
template<class First, class Second> int sum_ints_impl( std::pair<First, Second> const& p ) { return sum_ints_impl(p.first) + sum_ints_impl(p.second); }
int sum_ints_impl( int i ) { return i; }
template<class T> int sum_ints( T const& t ) { return sum_ints_impl( t ); }
<snip>
Can you show me how you would approach this problem?
The only solution I know is to make sum_ints_impl a concept itself with concept maps for int and std::pair. Frankly, I think that moving the metaprogramming into concepts like this is a terrible idea.
That seems to presume that the use case is inherently more-naturally addressed by metaprogramming than by generic programming. That may be true for some use-cases, but I wouldn't know how to identify them. It certainly does *not* seem to be true for Eric's example.
The current situation with template error messages may be bad, but I strongly suspect that the errors coming from such a concept metaprogramming system would be far worse, because of the "silently fail to match" behavior of concepts.
You lost me there. -- Dave Abrahams BoostPro Computing http://www.boostpro.com