[boost] Re: Proposal --- A type-safe union

From: Itay Maman (itay_maman_at_[hidden])
Date: 2002-06-12 14:48:55

Yitzhak Sapir wrote:
>>-----Original Message-----
>>From: Douglas Gregor [mailto:gregod_at_[hidden]]
> 
> 
> 
> 
> boost::any also allows an infinite range of types that may not necessarily be incomplete.  
 > For example, you could have a union of all types that inherit from 
some common base type (Shape),
 > or a union of any instantiation of a templated type
 > (I wonder if it is possible to check the existence of a class as part 
of a templated type
 > at compile time -- perhaps using the "has member" compile time test).
 >

The variant implementation relies on the ability to map concrete types 
to integers. My implementation uses the index_of TypeList algorithm, for 
instance.

So, unless we'll come-up with some birlliant way to do this mapping 
differently, we will not be able to implement a variant whose list of 
legal (concrete) types is 'open'.

-Itay