Re: [boost] compact_optional -- prompting interest

Subject: Re: [boost] compact_optional -- prompting interest
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2015-09-28 18:40:05

On 28/09/2015 21:05, Andrzej Krzemienski wrote:
>> No, I was suggesting to allow assignment of values of type T (i.e.
>> "opt = v;"). Having a named function like store_raw_value reduces the
>> need in the typedef but the syntax should still be simpler.
[...]
> In a way, this would mean and implicit conversion from T to
> compact_optional<T>. I do not want any kind of implicit conversion between
> the two (because the two are something different). I could offer:
>
> opt.raw_value() = some_T;

This is still clunky; either an implicit conversion or simply an 
additional assignment operator to permit the other syntax is better.

It's also logical -- an optional type is essentially a superset of the 
original type (in the case of boost::optional it's a precise superset, 
while in this case it's technically an equivalent set with one redefined 
value, but since that value is supposedly invalid for the original type 
it's still logically a superset).

The only real danger that I can see of supporting the direct assignment 
syntax is if someone explicitly assigns the sentinel value directly. 
But while that's bad style it shouldn't be undefined behaviour.