Re: [boost] Re: programming guidelines, prefer free functions

From: Milutin Jovanovic (miki_at_[hidden])
Date: 2000-08-17 12:50:16

I must be missing something. You just wrapped the Vector. Sure it is very
specialized wrapper, but that is what you did. The same could have been done
with a member function:

namespace joe {
  struct ExtendedVector : Vector {
    int size() { return Size(); }
  };
}

Miki.

----- Original Message -----
From: <jsiek_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Thursday, August 17, 2000 1:41 PM
Subject: [boost] Re: programming guidelines, prefer free functions

>
> Here's a concrete example of why free functions are so great.
>
>
============================================================================
==
>
> joe/Vector.h:
>   namespace joe {
>     struct Vector {
>       double operator[](int i);
>       int Size();
>     };
>   }
>
>
> suzy/VectorOps.h (version 1, using members):
>   namespace suzy {
>     template <class Vector>
>     vector_add(Vector& x, Vector& y, Vector& z) {
>       for (int i = 0; i < z.size(); ++i)
>         z[i] = x[i] + y[i];
>     }
>   }
>
> jeremy/solver.h
>   namespace jeremy {
>     solver(...) {
>       ...
>       joe::Vector x, y, z;
>
>       suzy::vector_add(x, y, z); // doh! won't compile because Size()
>                                  // is capitalized in joe's Vector
>       ...
>     }
>   }
>
>
============================================================================
==
>
>
> suzy/VectorOps.h (version 2, using free functions):
>   namespace suzy {
>     template <class Vector>
>     vector_add(Vector& x, Vector& y, Vector& z) {
>       for (int i = 0; i < size(s); ++i)
>         z[i] = x[i] + y[i];
>     }
>   }
>
>
> jeremy/solver.h:
>
>   // do the external adaptation trick: specialize the free function
>   int size(const joe::Vector& x) { return x.Size(); }
>
>   namespace jeremy {
>     solver(...) {
>       ...
>       joe::Vector x, y, z;
>
>       suzy::vector_add(x, y, z); // problem solved!
>       ...
>     }
>   }
>
>
> Ciao,
>
> Jeremy
>
> 
>
>
>
>