220 8335 <52C46F6D.7080303@gmail.com> article
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From: Matthew Woehlke <mwoehlke.floss@gmail.com>
Newsgroups: gmane.comp.lang.c++.isocpp.proposals
Subject: Re: Proposal: Default swap operation
Date: Wed, 01 Jan 2014 14:41:33 -0500
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On 2014-01-01 14:23, Thiago Macieira wrote:
> On quarta-feira, 1 de janeiro de 2014 10:26:19, Matthew Woehlke wrote:
>> Foo::~Foo() = default;
>
> This requires more typing than:
>
> Foo::~Foo() {}

True, though it does express intent more clearly :-). However, that 
exact point was why I mentioned in the previous mail that the dtor is 
not the best example.

(In some pedantic coding styles, '= default;' would be one line where 
'{}' would be mandated to be written '\n{\n}', thus 2 more lines :-).)

> And quite frankly I don't see the benefit. This destructor can't be from other
> translation units under the conditions you described.

Yes. This would need to be changed for the idea to be useful. So there 
is still something that could be changed here; specifying that '= 
default' should make the definition accessible to other translation 
units the same as if a user definition had been provided. (If it is not 
possible to change the behavior of '= default', then I would propose '= 
extern default' instead to explicitly specify that a symbol should be 
emitted.)

> This destructor cannot be trivial either under your condition: if all of them
> were trivial, then you could have left the declaration in the header.

Right. If '= default' appears in the .cpp and not in the .h, the 
compiler shall (be free to) assume that it is non-trivial. Because in 
practice, if you need it in the .cpp and not the .h it is likely 
(always?) because it is non-trivial anyway.

-- 
Matthew

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