[boost] Re: Singular variants?

From: Eric Friedman (ebf_at_[hidden])
Date: 2003-10-11 21:04:18

E. Gladyshev wrote:
> Besides singular variant is more basic.
> One can always implement 'unspecified content'
> variants using 'singular' variants.

Is this true? Please demonstrate. (Wrapping in a pimpl doesn't count.)

Anyhow, last night I thought of another solution. Variant will retain 
its current semantics, but boost::empty will be given priority as the 
fallback type, regardless of its location in variant's template 
parameter list.

For example, all of

   variant< boost::empty, int, string >
   variant< int, boost::empty, string >
   variant< string, boost::empty, int >
   variant< string, int, boost::empty >
   ...and so on...

would use boost::empty as the fallback type, regardless of the fact that 
int is also nothrow default-constructible.

Does this address your concerns, Eugene? I believe this is a better 
solution than allowing a singular state.

Eric