Sérgio Vale e Pace wrote:
Jonathan Turkanis wrote:
Two comments, though:
1. Your code breaks boost::any for use with non-OutputStreamable types.
that´s the odd part it didn´t. as long I don´t use the insert operator i works fine and I don´t understant why it don´t break. see:
class A {};
void foo() { A a; int b=0; any x; x = b; cout << x; b = any_cast<int>(x);
x = a; // cout << x; // as long as this line is commented everything works fine a = any_cast<A>(x); }
on the other hand if I do invoke the insert operator (<<) on a non-OutputStreamable type I get a stack overflow also I don´t understand why.
Anything is convertible to boost::any, and since you have an operator<< for boost::any, it will catch any object that doesn't have a better matched operator<< (i.e. any one that doesn't require a user defined conversion). If this didn't happen, you'd just get a compiler error when you tried to create an any<A>, since creation of that requires instantiation of all virtual functions of holder<A>, including the ill-formed print member (e.g. no overload matches the call out<<held). Dispatching to some kind of default call (which might just set failbit on the stream, or you could make it configurable) is probably the best way to handle this. Tom