"AlisdairM" <alisdair.meredith@uk.renaultf1.com> writes:
Jeremy Day wrote:
Personally I would prefer it if handlers automatically got the same order as would be provided by overload resolution. It's almost always a mistake to write
catch(Base&) { ... } catch(Derived&) { ... }
Surely it would be possible to reorder the type list that catcher uses (which it gets from the exception handling class, such as my_exception_handler) so that the order is always from most derived (such as Derived&) to least derived (such as Base&). Is there an MPL algorithm somewhere that will do that? I feel certain that I saw some code by Andrei Alexandrescu that did something along those lines.
Note the word 'almost' in Dave's statement ;?)
Don't read too much into that.
No, I don't know any GOOD reason to write catch clauses in Base/Derived order, but I can write code that will be caught by the derived handler:
struct my_exception : std::runtime_error, std::logic_error { ... };
void test() { try { throw my_exception(); } catch( const std::exception & ) {} catch( const std::runtime_error & ) {} }
Now the question is - can I find a good example with an exception hierarchy designed in this way, where catching on the derived type first would break code? In priciple I can fake up the example, but how likely is it to be a problem in real-world use?
Not. :) -- Dave Abrahams Boost Consulting www.boost-consulting.com