Re: [boost] storing intrusive_ptr in atomic?!

Subject: Re: [boost] storing intrusive_ptr in atomic?!
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2013-10-25 06:28:55

On Friday 25 October 2013 10:25:16 Giovanni Piero Deretta wrote:
> On Fri, Oct 25, 2013 at 10:22 AM, Oliver Kowalke
> 
> <oliver.kowalke_at_[hidden]>wrote:
> > 2013/10/25 Giovanni Piero Deretta <gpderetta_at_[hidden]>
> > 
> > > Intrusive_ptr doesn't have tivial copy constructor (how could it have?
> > > it
> > > needs to update the counter), ergo is not trivially copyable and the
> > 
> > above
> > 
> > > two point do not apply.
> > 
> > but the standard says 'trivially copyable' not 'trivial copy constructor'
> > -
> > e.g.
> > the code examples by the standard document gives correct results for
> > intrusive_ptr (because all criteria
> > are fulfilled).
> > does this mean the standard document contains a false wording/examples?
> 
> I do not have the standard at hand, but a trivially copyable class is a
> class that:
> 1. Has no non-trivial copy constructors (this also requires no virtual
> functions or virtual bases)
> 
> 2. Has no non-trivial move constructors
> 
> 3. Has no non-trivial copy assignment operators
> 
> 4. Has no non-trivial move assignment operators
> 
> 5. Has a trivial destructor
> 
> [from cppreference.com, which may or may not be authoritative]

You are correct, I'll just provide some references:

Trivially copyable types are defined in 3.9/9 [basic.types].

[...] Scalar types, trivially copyable class types (Clause 9), arrays of such 
types, and cv-qualified versions of these types (3.9.3) are collectively 
called trivially copyable types. [...]

Trivially copyable class types are defined in 9/6 [class].

A trivially copyable class is a class that:
— has no non-trivial copy constructors (12.8),
— has no non-trivial move constructors (12.8),
— has no non-trivial copy assignment operators (13.5.3, 12.8),
— has no non-trivial move assignment operators (13.5.3, 12.8), and
— has a trivial destructor (12.4).
A trivial class is a class that has a trivial default constructor (12.1) and 
is trivially copyable.
[ Note: In particular, a trivially copyable or trivial class does not have 
virtual functions or virtual base
classes. — end note ]