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From: Ville Voutilainen <ville.voutilainen@gmail.com>
Newsgroups: gmane.comp.lang.c++.isocpp.proposals
Subject: Re: Re: RFC: Adding Coherency Between any and optional<T>
Date: Tue, 3 Feb 2015 22:15:01 +0200
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On 3 February 2015 at 22:10, Nicol Bolas <jmckesson@gmail.com> wrote:
>> But you are OK with having the above problems with std::optional<std::any>
>> for example? (assuming 'any' has 'none' support)?
> It is a sticky issue: to have std::any which could store any value, and then
> wrap it in something who's comparison to a certain value has a special
> meaning.

That works just fine today.

> My suggested means of resolving that problem is to make it so that std::any
> cannot store a std::none object. After all, objects of std::none has no
> values. So its highly unlikely that any user would need to store one inside
> a std::any. And if they did, they could simply use a conditional switch or
> something.
>
> Similarly, optional<std::none> should be outlawed.

So, what does assigning none to an optional<any> mean? What is it assigning
to?

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