I've been doing some review of Andrei's book which has led me to trying to figure out how placement new works, or doesn't work. The new(address) Type syntax tells me "no allocator for TYPE". I did find information on "Class Allocators" at https://dlang.org/spec/class.html#allocators, but when I try to do things the Class Allocator way DMD tells me that "class allocators are obselete, consider moving the allocation strategy outside of the class". My best guess right now is that both class allocators and the placement new syntax are deprecated, but if that's the case I would expect a deprecation message when I try to use that new(address) Type syntax whether there's a class allocator present or not. Any insight into this? Thanks.

On Sunday, 31 January 2021 at 23:19:09 UTC, Kyle wrote:

> strategy outside of the class". My best guess right now is that both class allocators and the placement new syntax are deprecated, but if that's the case I would expect a deprecation message when I try to use that new(address) Type syntax whether there's a class allocator present or not. Any insight into this? Thanks.

Class allocators were deprecated in 2.080 and became an error in 2.087:

https://dlang.org/deprecate.html

I assume the placement new syntax was supposed to have been deprecated as well. It's possible it was overlooked, or that it wasn't deprecated because it has an obscure use-case that I'm unaware of. These days we should be using std.conv.emplace:

https://dlang.org/phobos/std_conv.html#.emplace.4

See also:

http://p0nce.github.io/d-idioms/#Placement-new-with-emplace

I suggest you file an issue at:

https://issues.dlang.org/

On Sunday, 31 January 2021 at 23:19:09 UTC, Kyle wrote:
> My best guess right now is that both class allocators and the placement new syntax are deprecated, but if that's the case I would expect a deprecation message when I try to use that new(address) Type syntax whether there's a class allocator present or not. Any insight into this? Thanks.

Yes, just use emplace() insead of placement new.

GC-less allocations however is up to you, either malloc/free, std.experimental.allocator or any other way. You can make your own smart pointer struct to handle this automatically, or better use community packages such as 'automem'.

As for the message it is possible that this part of the reference compiler was already passed deprecation period and should be removed but was completely forgotten.

https://dlang.org/phobos/core_lifetime.html#.emplace