Rust Code in the Wild

[Timon Gehr]

On 09/05/2013 05:22 AM, Meta wrote:
> While browsing Hacker News I came across this announcement of a physics
> engine written in Rust. Just browsing through the code, I noticed that
> it looks extremely arcane. I guess after awhile it's something you could
> get used to, but it seems somewhat ironic that the author says that C++
> will die of ugliness, when Rust already has syntactic monstrosities such
> as these:
>
> pub struct BodyWorld<N, LV, AV, M, II, CM> {
>      world: World<N, Body<N, LV, AV, M, II>, Constraint<N, LV, AV, M, II>>,
>      forces: @mut BodyForceGenerator<N, LV, AV, M, II>,
>      integrator: @mut BodySmpEulerIntegrator<N, LV, AV, M, II>,
>      detector: @mut BodiesBodies<N, LV, AV, M, II, BF<N, LV, AV, M, II>>,
>      sleep: @mut IslandActivationManager<N, LV, AV, M, II>,
>      ccd: @mut SweptBallMotionClamping<N, LV, AV, M, II, BF<N, LV, AV,
> M, II>>,
>      joints: @mut JointManager<N, LV, AV, M, II>,
>      solver: @mut AccumulatedImpulseSolver<N, LV, AV, M, II, CM>
> }
>
> This stuff is downright arcane.

Why? I cannot spot any syntax I wouldn't get used to quickly in this 
example. (AFAIK the @ are going away in favour of a library solution 
with more verbose syntax though.)

In D something similar would look like this:

struct BodyWorld(N, LV, AV, M, II, CM){
     World!(N, Body!(N, LV, AV, M, II), Constraint!(N, LV, AV, M, II)) 
world;
     BodyForceGenerator!(N, LV, AV, M, II)* forces;
     BodySmpEulerIntegrator!(N, LV, AV, M, II)* integrator;
     BodiesBodies!(N, LV, AV, M, II, BF!(N, LV, AV, M, II))* detector;
     IslandActivationManager!(N, LV, AV, M, II)* sleep;
     SweptBallMotionClamping!(N, LV, AV, M, II, BF!(N, LV, AV, M, II))* ccd;
     JointManager!(N, LV, AV, M, II)* joints;
     AccumulatedImpulseSolver!(N, LV, AV, M, II, CM)* solver;
}

Afaics there is not much of a difference. Arguably, having the 
identifiers conveniently aligned to the left is actually a slight 
advantage of rust's syntax.

Of course, the code contains a certain amount of duplication I wouldn't 
really want to write down, and this could be improved in D:

struct BodyWorld(N, LV, AV, M, II, CM){
     private alias Args = Seq!(N, LV, AV, M, II);

     World!(N, Body!Args, Constraint!Args)    world;
     BodyForceGenerator!Args*                 forces;
     BodySmpEulerIntegrator!Args*             integrator;
     BodiesBodies!(Args, BF!Args)*            detector;
     IslandActivationManager!Args*            sleep;
     SweptBallMotionClamping!(Args, BF!Args)* ccd;
     JointManager!Args*                       joints;
     AccumulatedImpulseSolver!(Args, CM)*     solver;
}