Re: [boost] [optional] How to define boost::none?

Subject: Re: [boost] [optional] How to define boost::none?
From: Sylvester-Bradley, Gareth (Gareth.Sylvester-Bradley_at_[hidden])
Date: 2014-11-19 10:40:57

Hi Andrey,

On Wed, Nov 19, 2014 at 3:27 PM, Andrey Semashev wrote:
> Since none has internal linkage, it is translation unit-specific.
> Technically, this can cause ODR violations in some cases. To avoid
> that you can declare it like this:
>
>  struct none_t {};
>
>   template< typename T >
>   struct singleton
>   {
>     static const T instance;
>   };
>   template< typename T >
>   const T singleton< T >::instance = T();
>

  // Do we need...
  namespace
  {

>   const none_t& none = singleton< none_t >::instance;

  }
  // ?

Thanks,
Gareth

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