09-Dec-2014 21:05, H. S. Teoh via Digitalmars-d пишет:
1. enums are hard to extend for std lib, and absolutely impossible by
3rd party libraries.
2. Single hierarchy has some appeal but it doesn't allow to catch on
similar classes that do not inherit from the same base class.
Basically there are many ways to view similarities of excpetions and
single hierarchy fails to address that.
If we were to replace each class with a base interface and every Kind
enum with an interface (inhereting from one or more base interfaces)
then we can actually address both of these points.
[...]
I like this idea!
[snip]
For example, dirEntries may fail due to permission failure, but the user
is generally not interested in OS-specific error codes like errno or
Windows error numbers; what is more interesting is "was this failure
caused by permission error?".
This problem cannot be satisfactorily resolved with a single Exception
hierarchy, but it *can* be resolved by using interfaces instead of base
classes. We could then have a WindowsException and a PosixErrnoException
(for example), and have subclasses also implement a NoAccessException
interface. Thus you have a class hierarchy based on implementation
details (e.g., PosixErrorException stores errno, and WindowsException
stores Windows error codes), but also an interface hierarchy based on
logical categorizations of exceptions.
That's exactly what I aim to do. The question is how hard it's do in
runtime and if there are any critical assumptions that prevent this.
--
Dmitry Olshansky
