On Wednesday, 21 December 2016 at 15:01:20 UTC, Eugene Wissner
wrote:
On Wednesday, 21 December 2016 at 14:15:06 UTC, John C wrote:
On Wednesday, 21 December 2016 at 11:45:18 UTC, Eugene Wissner
wrote:
This prints 3 times "Destruct" with dmd 0.072.1. If I remove
the if block, it prints "Destruct" only 2 times - the
behavior I'm expecting. Why?
Possibly to do with named return value optimisation.
Isn't an optimization that changes the behavior bad? I had a
crash in the code where the destructor did something
meaningfull, freed the memory (the same pointer) twice.
Basic stuff such as this is appropriately tested. The named
return value optimization is enforced by D (incl. unoptimized
builds), so behavior doesn't change by this optimization. It's
you who changed the behavior by removing the if. Due to the `if`,
the compiler doesn't know whether it should construct `a` or `b`
directly into the memory (sret pointee) provided by the caller.
When omitting the `if`, it's clear that `b` is returned in all
cases, so the compiles constructs `a` on the local stack (and
destructs it before exiting the function), but emplaces `b` into
`*sret` (i.e., the caller's stack) and can thus elide 1x postblit
+ 1x dtor.
