Re: [boost] N2346 - Defaulted and Deleted Functions emulation

Subject: Re: [boost] N2346 - Defaulted and Deleted Functions emulation
From: David Abrahams (dave_at_[hidden])
Date: 2009-03-02 09:18:06

on Sun Mar 01 2009, "vicente.botet" <vicente.botet-AT-wanadoo.fr> wrote:

> My concern is that:
>
>     #define BOOST_DEFAULT_CONSTRUCTOR_DEFAULT(T) inline T(){};
>
> emulates the syntax but not the semantics of
>
>     #define BOOST_DEFAULT_CONSTRUCTOR_DEFAULT(T) T()=default;
>
> The point of using the C++0x T()=default syntax is probably to ensure
> that the class is a POD.
>
> In C++03, the class designer has to make a design tradeoff. If
> providing a default constructor is more important than making the
> class a POD, then your emulation is OK. But if the priorities are the
> other way around, then the macro should just eliminate the default
> constructor.

Really the only likely use is to ensure POD-ness, because after all "{}"
is a lot easier to type and read than "=default;"

One thing we could do in the macro is to

  BOOST_MPL_ASSERT((boost::is_pod<T>))

Of course, if you know enough about your implementation you can
specialize boost::is_pod<YourType> (with the usual caveats if you get it
wrong).

I'm not sure it'd be worth it though.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com