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From: Daniel James <dnljms@gmail.com>
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Subject: Re: optional<T>, one more value or two states
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On 26 January 2013 18:01, Olaf van der Spek <olafvdspek@gmail.com> wrote:
> Op vrijdag 25 januari 2013 21:20:36 UTC+1 schreef Nicol Bolas het volgende:
>
>> And can be NULL.
>>
>> No, it can be empty, not NULL. `optional` is a container.
>
>
> Is it?
> The C++ container concept has a lot of requirements that optional doesn't
> meet.

But it could easily be changed to meet them. 'Optional' is a container
(in the wider sense) with a maximum of 1 element. It is not in any
sense a pointer. In fact, std::optional probably should meet the basic
container requirements, as it would allow it to be used with generic
functions.

>  I think using operator* is natural.

But it does currently imply certain semantics. The current situation
is that if you write:

    auto x = y;
    *x = 2;

Then for any standard type this is equivalent to assigning '2' to
whatever y points to. By using 'operator*' in std::optional, the
semantics of 'operator*' will be changed. That shouldn't be done
lightly, especially since with templates and 'auto' a type is defined
by the functions and operators that it supports..

-- 

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