Re: [boost] SafeInt code proposal

Subject: Re: [boost] SafeInt code proposal
From: Niels Dekker - address until 2010-10-10 (niels_address_until_2010-10-10_at_[hidden])
Date: 2009-06-23 15:22:57

Jean-Francois Bastien wrote:
> [pedanticism]
> Don't both your examples rely on pre-standard C++ friend declarations
> and definitions injecting the function name in the innermost enclosing
> namespace? I might be reading this worng, but 7.3.1.2 [namespace.memdef]
> paragraph 3 states: "The name of the friend is not found by unqualified
> lookup (3.4.1) or by qualified lookup (3.4.3) until a matching
> declaration is provided in that namespace scope".
> So you'd still need to declare in the namespace. From what I understand
> the examples shouldn't work.
> 
> Correct me if I'm wrong :)

Well... I do appreciate your pedanticism, but I think you're wrong.  All 
the compilers I tried accept the function calls to the inline friend 
function, operator-(safe_int,safe_int), including MSVC 2008 SP1, Comeau 
(www.comeaucomputing.com/tryitout), and g++ 4.1.2, run at 
http://codepad.org/dB9IbQJ7

You might want to have a look at [temp.inject] ("Friend names declared 
within a class template"). Quoting the latest C++0x Working Draft, 
www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2857.pdf, 14.7.5/2 
(slightly reformatted):

"As with non-template classes, the names of namespace-scope friend 
functions of a class template specialization are not visible during an 
ordinary lookup unless explicitly declared at namespace scope (11.4). 
Such names may be found under the rules for associated classes (3.4.2). 
[ Example:

   template<typename T> struct number {
     number(int);
   friend number gcd(number x, number y) { return 0; };
   };

   void g() {
   number<double> a(3), b(4);
   a = gcd(a,b); // finds gcd because number<double> is an
   // associated class, making gcd visible
   // in its namespace (global scope)
   b = gcd(3,4); // ill-formed; gcd is not visible
   }
—end example ]

Kind regards, Niels