Re: [boost] [optional] Safe optional

On Tue, Nov 18, 2014 at 12:24 PM, Nevin Liber wrote:

On 18 November 2014 01:16, Matt Calabrese wrote:

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On Mon, Nov 17, 2014 at 10:59 PM, Vicente J. Botet Escriba < vicente.botet@wanadoo.fr> wrote:

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I will ad that I believe Dr BS don't like dynamic visitation, but

here

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we are doing pattern matching on types, isn't it?

For a while I assumed exactly that, but he actually specifically voiced that he does not like visitation on variant and thinks of it as a hack. It's sad :/

FWIW: I think he is (a) correct, but (b) we have nothing better to replace it, so we still need it.

We should really start a thread about this. I'm very curious to see an actual objective rationale both for why visitation over a closed set of types known at compile time is in any way a "hack," along with a realistic alternative. It really is a fundamental operation of a discriminated union. As someone who uses variants pretty much as the "default" for run-time polymorphism in day-to-day coding, I have never seen an actual explanation for what someone might consider bad about variant visitation, neither from Bjarne nor anyone else.