Exceptions in @nogc code

[Andrei Alexandrescu via Digitalmars-d]

Walter and I discussed the following promising setup:

Use "throw new scope Exception" from @nogc code. That will cause the 
exception to be allocated in a special stack-like region.

If the catching code uses "catch (scope Exception obj)", then a 
reference to the exception thus created will be passed to catch. At the 
end of the catch block there's no outstanding reference to "obj" so it 
will be freed. All @nogc code must use this form of catch.

If the catching code uses "catch (Exception obj)", the exception is 
cloned on the gc heap and then freed.

Finally, if an exception is thrown with "throw new Exception" it can be 
caught with "catch (scope Exception obj)" by copying the exception from 
the heap into the special region, and then freeing the exception on the 
heap.

Such a scheme preserves backward compatibility and leverages the work 
done on "scope".


Andrei