[boost] Re: Programming by contract

From: Dirk Gerrits (dirk_at_[hidden])
Date: 2002-10-27 13:15:28

Martin wrote:

> Hi
>
> Does anybody have any ideas or pointers to how programming by contract can
> be implemented easily in C++? I can only think of one non-elegant solution
> which involves defining a class in the function that is derived from a
> template class. something like this (not fully implemented):

[code omitted]

>
> This example does not handle any arguments for the function. Anyway, I 
> would
> appreciate any comments or ideas on this topic.

How about a slight change to the run member function:

namespace boost
{
     template<class result_type>
     class contract
     {
     public:
         result_type run()
         {
             precondition();
             struct postcondition_guard
             {
                 explicit postcondition_guard(contract& c) : m_c(c) {}
                 ~postcondition_guard() { m_c.postcondition(); }
                 constract& m_c;
             };
             postcondition_guard guard;
                 return body();
         };
         virtual void precondition() {};
         virtual void postcondition() {};
         virtual result_type body() = 0;
     };
};

This way, there's no need for the extra copy of the result type.

Also, I think there are const-correctness issues. The above won't work 
if you'd like body to be a const member function. And shouldn't pre- and 
postcondition be const member functions?

Further, is there any reason why you put the assert in pre- and 
postcondition? Couldn't contract just as well do assert(precondition) 
and assert(postcondition)?

This is a start, but I'm sure a better solution will pop-up somewhere 
along this thread. ;)

Regards,
Dirk Gerrits