Re: [boost] Formal review for QVM

Subject: Re: [boost] Formal review for QVM
From: Agustín K-ballo Bergé (kaballo86_at_[hidden])
Date: 2015-12-14 19:27:03

On 12/14/2015 9:07 PM, Emil Dotchevski wrote:
> On Mon, Dec 14, 2015 at 3:16 PM, Agustín K-ballo Bergé <
> kaballo86_at_[hidden]> wrote:
>
>> On 12/14/2015 7:57 PM, Emil Dotchevski wrote:
>>
>>> On Mon, Dec 14, 2015 at 1:12 PM, Agustín K-ballo Bergé <
>>> kaballo86_at_[hidden]> wrote:
>>>
>>> On 12/14/2015 5:53 PM, Emil Dotchevski wrote:
>>>>
>>>> On Mon, Dec 14, 2015 at 4:46 AM, Agustín K-ballo Bergé <
>>>>>
>>>>> if the compiler says there is an error here because `normalized` needs a
>>>>
>>>>> default constructor, I'm gonna start suspecting something wrong is going
>>>>>> on
>>>>>> with the library. This is what I would naively expect `normalized` to
>>>>>> be
>>>>>> doing:
>>>>>>
>>>>>>       template <typename Vec>
>>>>>>       Vec normalized(Vec v) {
>>>>>>         return v /= length(v);
>>>>>>       }
>>>>>>
>>>>>>
>>>>> It can't be implemented that way because the type of the argument might
>>>>> not
>>>>> be copyable.

[snip]

>>
>> Views are special, that has already been established. My question was not
>> in regard of views, whose case I said is unsurprising. My question was with
>> respect to this simple guy requiring the presence of a default constructor:
>>
>>      myvec3 n = normalized(myvec3(1, 2, 3));

[snip]

>> Why does this guy require a default constructor? I understand now that it
>> doesn't, you simply don't want to handle this case any different than you
>> already do views. There's nothing wrong with that.
>
>
> I'm not sure if we're on the same page. I'll try again. :)

[snip]

> But in the end, normalized must return an object -- and it can't use a copy
> constructor (different types). And since I've never encountered a vector
> type without a default constructor, it seemed reasonable to not worry too
> much about requiring it.

Yep, that sums it up. There's cases were the need for a default 
constructor is artificial since a copy constructor could be used, but 
special-casing that is not worth the trouble.

Regards,
-- 
Agustín K-ballo Bergé.-
http://talesofcpp.fusionfenix.com