On Friday, 19 September 2014 at 07:57:24 UTC, Dicebot wrote:
I am obviously in favor of simply calling recurrent mutable
exception chains illegal (probably even immutable ones until we
fix const correctness of druntime exception handling).
Reason is simple : it doesn't require any changes in existing
code and is exactly the way we already do it in Sociomantic :)
To make it reliable Exception chain may need to be updated to
doubly-linked list to be able to efficiently verify that new
exception is not already present in the chain. I don't see any
costly overhead implications from that though.
That might be sufficient for a particular application like
Sociomantic's, but it's not sufficient for library code in
general. Such chains aren't logic errors and can easily occur in
the wild.
The point of exception chaining is so exceptions can be thrown in
destructors and such. In library code, these destructors don't
know what exception is in flight, so they can only assume it
could be any exception. If self-referencing chains were illegal
and exceptions were statically allocated, then the conclusion is
that these destructors can't throw anything after all, because
that exception might already be in flight. As such, exception
chaining would be completely useless.
