Vectors and matrices in D

[Bill Baxter]

Andreas Zwinkau wrote:
>> I started implementing a little raytracer in D (raytracing is addictive, yeah ;)), and faced problems with vector/matrix math :(
> 
> Me too :)
> I wanted to learn D and to write a raytracer for some time. Currently i have some time to do so. I got a little sidetracked into D templates by the vector implementation.
> 
> Every implementation (Artyom, helix, some C++ raytracers) i've seen so far uses a struct for the vectors. Why? Performance? Does Bill Baxter hint at this?
> http://www.digitalmars.com/pnews/read.php?server=news.digitalmars.com&group=digitalmars.D&artnum=46958
> 
> I wrote a generic vector class. Maybe someone would like to comment on that? I it's just addition and subtraction so far, but the pattern is clear. Here comes my code:
> 

I think the reason people use structs for Vector types is because 
structs are for Plain Old Data, and Vectors are Plain Old Data.  Mainly 
the differences that they're constructed on the stack by default which 
is generally what you want with something like a Vector (for 4-vectors 
and lower at least).  Other things also make them more struct like -- 
you want A = B to make a copy of B, not make a second reference to the 
same B.  You don't need to be able to subclass them.

The main problem is that passing big structs by value as parameters is 
kind of slow.  And it's something you want a lot.  In C++ you'd use 
const& Vector for the argument types, but in D there's no equivalent.

The good thing about using classes is that they're passed by reference 
by default.  But that's about the only good thing about them in this 
context.

Allocations on the heap can be slow.  Using 'scope' can get you around 
that, but then you'll be using "scope Vector this",  "scope Vector that" 
all the time and it will get tiresome.

Anyway, if you're coming from Java then doing a heap allocation for 
every vector may not seem like a big deal.  But Java's allocations of 
small objects are pretty heavily optimized from what I've heard.  D 
isn't really there.

Sorry if this is incoherent... I probably should have gone to be an hour 
ago.

--bb