Re: [boost] SafeInt code proposal

Subject: Re: [boost] SafeInt code proposal
From: Jean-Francois Bastien (jfbastien_at_[hidden])
Date: 2009-06-23 15:56:20

Niels,

> 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 ]

I might very well be wrong, that part of the standard has always been a bit shady to me and had a ring of "pre-standard stuff". That being said compilers aren't the best way to verify standard compliance ;)

>From the section you quote some of the lookup rules do apply while others not, but only for templates. If I remember that was used before template templates existed.

Sorry for being OT, curiosity bit me :)