Re: [boost] [optional] Safe optional

Subject: Re: [boost] [optional] Safe optional
From: Vladimir Batov (Vladimir.Batov_at_[hidden])
Date: 2014-11-19 16:36:16

On 11/20/2014 08:22 AM, Vladimir Batov wrote:
>
> On 11/19/2014 07:37 PM, Andrzej Krzemienski wrote:
>
>> ...
>> optional<double> Aircraft::weight()
>> {
>>    if (Impl* impl = get_impl())
>>      return impl->compute_weight();
>>    else
>>      return none;
>> }
>>
>> double Aircraft::max_weight()
>> {
>>    return 10000.0;
>> }
>>
>> bool too_heavy(Aircraft& ac)
>> {
>>    return ac.weight() > ac.max_weight();
>>    // in "safe" optional compiler would spot the bug
>> }
>
> There is no bug here! Not from the human perspectives. You are 
> comparing two extremely closely related types! As long as we agree on 
> how "none" is treated, then all kosher. We do compare "ints" with 
> "doubles", don't we? No "safety" concerns.

On the second thought I might probably agree that op<() might be 
questionable... Can we address that differently then? Say,

bool operator<(T const&, optional<T> const&) { BOOST_STATIC_ASSERT(); }