From: Vladimir Prus [mailto:ghost@cs.msu.su] Hi, I just had a couple of bugs caused by the fact that constructor of boost::any is not explicit. For example:
void do_something(boost::any& v) { ... }
class variable { ///// boost::any& value() {} };
variable v; do_something(v);
The intention was to call do_somethin on 'v.value()' but non-explicit ctor is happy to accept 'variable', after which 'do_something' breaks.
Anybody has an opinion? Is non-explicit ctor really necessary?
(Note that the example above avoids the issue of implicit conversion (it won't compile), because it takes the parameter by non-const reference. With the current implementation, this is a good trick to use.) I agree that the constructor should be made explicit. I seem to recall that we discussed this on the list about a year ago, and the main objection against an explicit constructor was that the behavior across different compilers wasn't consistent (some compilers didn't like explicit template constructors at all). But now, a year later, perhaps it's time to go ahead and make the change? It's unfortunate that it's a change that will break code; perhaps some legacy mode needs to be provided. Anyway, there have been several requests for this and thus far no strong opinions against it. Bjorn