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From: Chris Jefferson <chris@bubblescope.net>
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Subject: Re: optional<T>, one more value or two states
Date: Thu, 24 Jan 2013 14:05:58 +0000
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On 24/01/13 13:52, Zhihao Yuan wrote:
> On Thu, Jan 24, 2013 at 7:38 AM, Ville Voutilainen
> <ville.voutilainen@gmail.com> wrote:
>> I have since cured that problem in my head, there's no 'danger' involved in
>> it.
> The danger already shows up.
>
> Quoting from the proposal:
>
>    "Such implicit conversions impose some risk of introducing bugs,
>     and in fact in order to avoid one such possible bug we had to 'poison'
>     comparisons between optional<T> and T."
>
> And a carefully specified comparison logic is under discussion.
>
>> boost::optional has such implicit conversions, and I see no reason
>> to do it differently for std::optional.
> This is convincible to some (or many) people, but not me.
> Not all Boost practices are good.  They are not good just because
> they exists for several years.

True. But looking at the boost mailing list and bug reports, there does 
not appear (from what I could find, and remember) to have been any 
complaints about this. We certainly shouldn't ignore implementation 
experience.

I have written quite a lot of code with boost::optional, it is very 
common to make an optional<T> from a T, in 'return' statements for 
example. Having to add an explicit cast to all of those would annoy me.

Chris

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