Re: [boost] variant - off topic

Subject: Re: [boost] variant - off topic
From: Robert Ramey (ramey_at_[hidden])
Date: 2019-04-03 22:56:03

On 4/3/19 2:58 PM, Andrzej Krzemienski via Boost wrote:

>> So - simple proposal.  Require that sum types have operator= deleted.
>>
>> Robert Ramey
>>
> 
> It is an interesting observation. I am not sure about the consequences,
> though. 

Right - hence the motivation for my post.

It is not only assignment. I ti s also swap. STL algorithms, such
> as sort() use assignment and swap inside. The question is: should std::sort
> on variants work? 

Just the kind of example I was hoping to get.

This would raise the question: Under what circumstance would one want to 
do this?  Of course definition of a comparison function would be 
non-trivial. Or maybe this should be the red flag which says "you don't 
really want to do that".

> Or because of the special properties of a variant some
> STL algorithms should break, maybe storage in containers should be
> prohibitted? 

For sure, the assignment of such containers would be banned.

interestingly I could also envision storage in containers without 
sorting being supported.  But then as far as I know, all containers 
require that the member type be assignable?  So by deleting the 
assignment operator - these would already be prohibited with a concept 
check.

> Regards,
> &rzej;
> 
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