On 9/20/18 6:48 AM, Atila Neves wrote:
On Wednesday, 19 September 2018 at 21:16:00 UTC, Steven Schveighoffer
wrote:
Given dip1008, we now can throw exceptions inside @nogc code! This is
really cool, and helps make code that uses exceptions or errors @nogc.
Except...
The mechanism to report what actually went wrong for an exception is a
string passed to the exception during *construction*. Given that you
likely want to make such an exception inside a @nogc function, you are
limited to passing a compile-time-generated string (either a literal
or one generated via CTFE).
<snip>
I expressed my concern for DIP1008 and the `msg` field when it was first
announced. I think the fix is easy and a one line change to dmd. I also
expressed this on that thread but was apparently ignored. What's the
fix? Have the compiler insert a call to the exception's destructor at
the end of the `catch(scope Exception)` block. That's it. The `msg`
field is just a slice, point it to RAII managed memory and you're good
to go.
Give me deterministic destruction of exceptions caught by scope when
using dip1008 and I'll give you @nogc exception throwing immediately.
I've even already written the code!
I thought it already did that? How is the exception destroyed when
dip1008 is enabled?
But this means you still have to build msg when throwing the
error/exception. It's not needed until you print it, and there's no
reason anyway to make it allocate, even with RAII. For some reason D
forces msg to be built, but it does't e.g. build the entire stack trace
string before hand, or build the string that shows the exception class
name or the file/line beforehand.
-Steve
