Re: [boost] Feature request: variant::view

Subject: Re: [boost] Feature request: variant::view
From: TONGARI J (tongari95_at_[hidden])
Date: 2016-06-19 10:09:10

2016-06-19 21:54 GMT+08:00 Klemens Morgenstern <klemens.morgenstern_at_[hidden]>
:

> Am 19.06.2016 um 15:31 schrieb TONGARI J:
>
>> Hi,
>>
>> Sometimes we need to view a value as a variant and we don't want to copy
>> the value into a variant.
>>
>> It'd be great if there's a variant::view that works like a variant but
>> holds a reference to the value instead.
>>
>> The constructor should allow any reference to the types as in the variant,
>> and a constructor that takes a  reference to the variant, e.g.
>>
>> template<class T1, class T2...>
>> class variant<T1, T2...>::view
>> {
>>     view(T1&);
>>     view(T2&);
>>     ...
>>     view(variant&);
>> };
>>
>> And we can use apply_visitor/get on a view as on a variant.
>>
>> Thoughts?
>>
>
> Why not boost::variant<T1*, T2*> ?
>
> I guess boost::variant<boost::none, T1&, T2&> would also work
> (boost::none, if it needs to be default-constructible)
>
> Or do you need to use the same visitors?
>

Same visitor. Thanks for reminding me, variant<T1&, T2&> is close to my
intent, but probably suboptimal, I think it needs to visit the types to
convert to variant<T1, T2>.
For a view, it's just a discriminator assignment.