any_function: bcc 5.5.1; explicit ctor

From: Vladimir Prus (ghost_at_[hidden])
Date: 2001-03-28 02:59:33

1. I have just downloaded the most recent version of any_function, which 
documentation says it compiles under bcc 5.5.1, but it doesn't! The following 
simple code fails to compile:

        #include <boost/any_function.hpp>

        void foo(int) {}
        int main() 
        {
                boost::any_function<void, int> v;
                v = foo;
        }

The problem seems to be in using enums for constants in various places. 
Consider:

        template<int i> struct I { enum { val = i }; };
        template<int i> struct V {};

        template<int i>
        struct S {

                enum { val = I<i>::val }; 

                typedef V<val> type;     //  1
        };

Given this declarations, bcc thinks that S<23>::type is ... V<0>! This is 
cleary bug, which affects any_function.hpp. I'm not sure if it can be 
workarounded, leaving enums, but one can change val to static const int 
member, and change line #1 to 
        typedef V<int(S::val)> type;
This will work. I actully wonder why enum is used for const values. Is there 
any other compiler that has problems with static const ints?

2. I found explicit ctor of any_function not very good idea.
        -	It adds no safety at all, but is a big encumbrance.
        -	Is it reasonable to make ctor explicit while permitting assigment
                without explicit conversion? Don't you think that if conversion of type
                A to type B is considered dangerous, then both marked lines should not 					
                compile?
                        struct S { 
                                S();
                                S(const B& b) : b(b) {};
                                B b;
                        };
                        A a;
                        S s1(a);		//*
                        S s2;
                        s2.b = a;	//*	
                

-- 
Regards,
Vladimir