Re: [lmi] depr.impldec

[Greg Chicares]

On 7/28/22 00:29, Vadim Zeitlin wrote:
> On Wed, 27 Jul 2022 19:55:32 +0000 Greg Chicares <gchicares@sbcglobal.net> 
> wrote:
> 
> GC> On 7/13/22 20:51, Greg Chicares wrote:
> GC> [...]
> GC> > I weakly favor the Rule of Zero, while you more strongly favor
> GC> > the Rule of Five, so let's start with a universal Rule of Five
> GC> 
> GC> I've changed my opinion.
[...]
>  One benefit that I hadn't mentioned yet, I think, is that if you ever
> define a special member in your class, e.g. decide to do something in the
> default ctor, it would silently inhibit moving. This should, arguably,
> happen only rarely, but I guarantee that if it does happen, it will remain
> unnoticed for a long time.

Unless we guarantee that it cannot happen, e.g., with "concept" assertions.
But you mentioned that technique in another thread, where I'll reply soon.

>  Also, there are many important exceptions, e.g. you still have to write
> all 5 special members for any polymorphic base classes

But we can write them all once...

  #include "crtp_base.hpp"

...and only once:

  class A : private lmi::polymorphic_base<A> {};
  static_assert( std::is_polymorphic_v           <A>);
  static_assert( std::is_default_constructible_v <A>);
  static_assert( std::is_destructible_v          <A>);
  static_assert( std::is_copy_constructible_v    <A>);
  static_assert( std::is_move_constructible_v    <A>);
  static_assert( std::is_copy_assignable_v       <A>);
  static_assert( std::is_move_assignable_v       <A>);

(and those assertions can be combined into one "concept").