Re: [boost] Formal review request: static size matrix/vector linear algebra library (Boost) LA

Subject: Re: [boost] Formal review request: static size matrix/vector linear algebra library (Boost) LA
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2010-02-10 20:59:08

2010/2/10 Agustín K-ballo Bergé <kaballo86_at_[hidden]>:
> El 09/02/2010 03:45 a.m., Emil Dotchevski escribió:
>> 2010/2/8 Agustín K-ballo Bergé <kaballo86_at_[hidden]>:
>>> boost::la::la_detail::vref_< T > get( int index )
>>> {
>>>    return boost::la::vref( ... );
>>> }
>>
>> I was actually interested in the ... part :)
>
> It's merely an expression that returns a T(&)[N].

Ah, I see. I'd just return T(&)[N] as in the code from my previous
post; T(&)[N] is a conforming type already. You only need vref if all
vectors/matrices in an expression are of built-in types:

float v1[3] = { .... };
float v2[3] = { .... };
v1*v2; //error; you need vref(v1)*v2.

but:

float v1[3] = { .... };
boost::la::vec<float,3> v2=....;
v1*v2; //okay

> I have been bitten by the precedence issue to the point I enclose every
> pipe operation in parenthesis. And it gets worse if "complex swizzling
> expressions" are added to the library. Consider
>
> ( v1 | ( Y, -X ) ) * 2;

I don't think that such syntax is acceptable. I have to think about
this but it seems to me that v1|Y-X should be possible (the currently
supported syntax, for "non-complex" swizzling isn't v1|(Y,X), it is
v1|YX.)

Or we can throw op| out the window, I do hate it. Perhaps the best
approach is to just use a function:

vbind<YX>(v1)

and let the user overload something if they want to.

> It *might* be possible to get ride of the precedence problems by using
> expression templates, but even then subscripting operator seems more
> natural.

Operator [ ] is the best choice, but it can not be overloaded
generically because it is required to be a member, for reasons that
are beyond my understanding of C++.

Emil Dotchevski
Reverge Studios, Inc.
http://www.revergestudios.com/reblog/index.php?n=ReCode