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 :)