Re: [boost] [qvm] Terseness of syntax etc.

Subject: Re: [boost] [qvm] Terseness of syntax etc.
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2015-12-09 18:58:17

On Wed, Dec 9, 2015 at 3:41 PM, Vicente J. Botet Escriba <
vicente.botet_at_[hidden]> wrote:

> Le 09/12/2015 13:43, Agustín K-ballo Bergé a écrit :
>
>> On 12/8/2015 1:25 PM, Phil Endecott wrote:
>>
>>> Adam Wulkiewicz wrote:
>>>
>>>> The formal review of Emil Dotchevski's QVM library begins today on 7th
>>>> Dec and ends on 16th Dec.
>>>> Full documentation is also viewable on Github:
>>>> http://zajo.github.io/boost-qvm/
>>>>
>>>
>>> I find most of the identifiers too short.  To give just a couple
>>> of examples: "transp" is used to mean "transpose".  You save
>>> typing three letters, and get confusion with transparent,
>>> transport, etc.  Then look at the names of some traits classes;
>>> elsewhere we have type_traits, allocator_traits, iterator_traits
>>> etc. all spelt out in full, but in qvm we have q_traits, v_traits
>>> and m_traits.  I could go on but really almost every identifier
>>> is too short for my tastes.
>>>
>>
>> I used an earlier version of the library several years ago, back when it
>> was called "Boost.LA", and I found extremely short identifiers to be a
>> concern too. I could understand going for `mat` and `vec` instead of
>> `matrix` and `vector`, but not just `m` and `v`. For pretty much every
>> other identifier, I would like to see a full blown word instead.
>>
> I'm not sure we need the prefix nor the suffix. The operations shouldn't
> have the type on its name.
> If the operation depends on a concept (vector, matrix, quaternion) and the
> operation has no parameter of this type the function should have the type
> as parameter
>
> What would be wrong replacing
>
>     float vmag = mag(v);
>     float33 m = rotx_m<3>(3.14159f);
>     vref(v,YXZ) = rotx_m<3>(3.14159f) * v;
>
> by
>
>     int mag = magnitude(v);
>     float33 m = rotate_x<M3>(3.14159f);
>     ref(v).YXZ() = rotate_x<M3>(3.14159f) * v;
>

Let me point out first that in this library q always means quaternion, m
always means matrix, and v always means vector. With that in mind, could
rotx_m<3> be misinterpreted?

Secondly, the semantics of rotx_m are different from what you're imagining.
It does *not* return a "proper" matrix object, it returns a reference to
its argument reinterpreted as an unspecified non-copyable 3x3 matrix type,
which essentially allows the passed angle (3.14159f) to participate as a
3x3 matrix in QVM operations without creating a temp. That's why when
instantiating the rotx_m template you specify the dimensions but not the
type of the matrix (of course you can assign the result to any compatible
matrix type.)

I'm really not a fan of the old operator% and now operator, syntax.
>>> To me, (v,XY) looks like you're forming a row-vector with two elements.
>>> Is there a reason why these accessors can't be written with function
>>> syntax, i.e. XY(v) ?  Or, for matrices, something like element<4,2>(m)
>>> rather than (m,A<4,2>) ?
>>>
>>
>> The precedence issues are so bad with `operator,` that one has to pretty
>> much always wrap it in parens, that makes all precedence issues go away. I
>> think for that reason it's a better choice than `operator%`, that mostly
>> just works and bit me over and over again. There are reasons against it
>> too, for instance a missing include, a typo, a shadowing variable will turn
>> a swizzling expression into a regular comma expression.
>>
>> That said, if I have to write `(v,XY)` instead of `v.XY` I'd rather write
>> `XY(v)` instead.
>>
>>
> Clearly the operator, is too controversial.
>
> Isn't
>
>     qvm::ref(v).XY()
>
> terse enough?
>

Compared to (v,XY)?

Emil