> Traditional C++ exceptions have two main problems:
> 1) the exceptions are allocated in dynamic memory because of inheritance and because of non-local constructs like std::current_exception. This prevents basic optimizations like transforming a throw into a goto, because other parts of the program should be able to see that dynamically allocated exception object. And it causes problems with throwing exceptions in out-of-memory situations.
> 2) exception unwinding is effectively single-threaded, because the table driven unwinder logic used by modern C++ compilers grabs a global mutex to protect the tables from concurrent changes. This has disastrous consequences for high core counts and makes exceptions nearly unusable on such machines.
That's really interesting. I've become very anti-exceptions in recent years far various much-discussed reasons (eg hard to follow, false economy, difficult if not impossible to write threadsafe C++ code in particular, use of exceptions as flow control is an anti-pattern).
One of the porposals is a value-or-error type object, which is basically what Rust has. I really like Rust's enums and match expressions.
It seems so difficult to make changes like this to C++ at this point, at what point do you just have to start again?