On Sunday, 2 June 2019 at 06:59:02 UTC, Jonathan M Davis wrote:
Almost certainly, hasElaborateCopyConstructor should be updated to test for both postblit constructors and copy constructors, since its purpose is to test for whether the type has a user-defined copying function [...] Whether hasElaborateCopyConstructor was the best name is debatable, but it _does_ involve "elaborate" copying, and copy constructors weren't actually in the language at the time. The documentation is wonderfully confusing though in that it talks about copy constructors and then says that a copy constructor is introduced by defining this(this) for a struct. So, it basically calls a postblit constructor a copy constructor.
I've made the mistake in the past of trying to use hasElaborateCopyConstructor to test for the presence of __xpostblit, and I'm sure I'm not the only one. The name is quite misleading--even more so now that D has real copy constructors.
If std.v2 ever materializes, we'll have an opportunity to fix papercuts like this. Until then, my preferred workaround is to use a renaming import:
import std.traits: hasNontrivialCopy = hasElaborateCopyConstructor;
