AMDG Steve Karmesin wrote:
A second issue has to do with capturing and rethrowing exceptions. This is a very cool capability but the implementation is limited because it can't detect and use user derived subtypes of the system exception types. This can be done with external polymorphism and would be a significant improvement.
Instead of storing a runtime_error store a pointer to an internal abstract base class such as untyped_exception_wrapper. Derive from that a templated class exception_wrapper that stores the user's type and can rethrow that type.
Then the set_exception member can be template and the exception type, wraps it with exception_wrapper and stores the pointer to the abstract base.
Then when the user goes to get the value from the future and it finds that there was an exception, it calls the rethrow method on the abstract base, the templated derived class does the concrete rethrow of the user's type and the user can then catch that type. This way the future library can catch and rethrow exceptions of types that it knows nothing about.
Below is some demonstration code for this pattern.
This functionality is already in Boost. http://www.boost.org/libs/exception/doc/tutorial_exception_ptr.html In Christ, Steven Watanabe