On Wednesday, 23 May 2018 at 13:12:57 UTC, Steven Schveighoffer
wrote:
On 5/22/18 9:59 PM, sarn wrote:
* Some code uses __dtor as a way to manually run cleanup code
on an object that will be used again. Putting this cleanup
code into a normal method will cause fewer headaches.
Using __dtor is a very bad idea in almost all cases. Putting
cleanup code into a normal function can have some of the same
pitfalls, however (what if you forget to call the super version
of the method?). The only *correct* way to destroy an object is
to follow the runtime's example or call the function directly.
The destructor also has the nice feature of being called when
the struct goes out of scope.
Best advice -- just use destroy on types to clean them up.
Here's an example of what I'm talking about:
https://github.com/dlang/phobos/blob/master/std/signals.d#L230
It's running __dtor manually just to run some code that happens
to be in the destructor. It's obviously not meant to run any
other destructors (at least, the documentation doesn't say "Use
this mixin in your object and then calling disconnectAll() will
destroy everything in your object.").
It's a broken design pattern, but existing code is doing it. (As
I said, I reviewed a lot of D packages, and I don't have time to
file bug reports or PRs for each one.)
But this is not necessarily the definition of POD. Generally
this means it has no postblit, and some people may even be
expecting such a thing to have no methods as well. So I'm not
sure we want to add such a definition to the library.
The common case is that some data types can be blitted around as
raw memory without worrying about destructors, postblits, or
whatever is added to the language in future. This is the thing
that seems to matter. (Have you seen any code that needs to care
if a struct has methods? It sounds like a very special case that
can still be handled using current compile-time reflection
anyway.)
__traits(isPOD) seems to do the job, and is a lot better than the
ad hoc implementations I've seen. We should encourage people to
use it more often.
