Re: [boost] [review][variant2] Variant2 Review Starts April 1

On 3/26/19 1:10 PM, Matt Calabrese via Boost wrote:

On Tue, Mar 26, 2019 at 2:03 PM Larry Evans via Boost wrote:

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On 3/26/19 12:08 PM, Andrzej Krzemienski via Boost wrote: [snip]

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As long as there are non-trivial trade-offs for any type/template, there will be reasonable users who would opt for different trade-offs when in different domains. We just have to decide which combinations of the trade-offs are worth collecting into a facility that is present in boost or the standard or elsewhere.

True. And maybe names of different variants of variant should reflect the different trade-offs. Maybe noempty::variant rather than variant2::variant?

What about:

template struct boost::variant2: std::variant { ... };

?

After all, isn't boost::variant2 simply more restrictive than std::variant in that boost::variant2 has the the never-valueless requirement but std::variant does not.

That cannot work for a variety of reasons. Even if it were possible to implement it that way and we were okay with a dependence on the standard library having std::variant, it also would mean that interactions with the variant via the base class would be able to break the child class's never-empty guarantee (meaning it would not be a guarantee). So an inheritance relationship here would not make sense.

Good point. Then how about: template struct boost::variant2 : private std::variant { using std::variant:: //{ all member functions **not** breaking never-valueless}; //{ over-rides for those member functions that **do** break never-valueless} //} };