Re: [boost] [core/noncopyable][test/boost::unit_test::singleton] massive test failures

Subject: Re: [boost] [core/noncopyable][test/boost::unit_test::singleton] massive test failures
From: Peter Dimov (lists_at_[hidden])
Date: 2014-08-21 15:25:51

Agustín K-ballo Bergé wrote:
> I see trivially copyable as a permission to use memcpy/memmove to replace 
> what would be a copy/move-construction, copy/move-assignment, and other 
> operations derived from them (say swap) **if** the corresponding special 
> member is provided and accessible.

If you never use is_trivially_copyable alone and always qualify it with && 
is_copy_constructible, I can see why you wouldn't mind 
is_trivially_copyable<X> to be true while is_copy_constructible<X> to be 
false.

But the other side of the coin is that in this case you simply do not care 
about what is_trivially_copyable returns. So there is no reason to object if 
is_trivially_copyable returns false for noncopyable types.

Of course... you will counter that your uses of is_trivially_copyable are 
sometimes qualified not by is_copy_constructible, but by 
is_move_constructible.

I admit that it is in principle possible for a trivially copyable, but 
noncopyable, type to have an accessible move constructor. Specific examples 
elude me as usual. :-)