generic + numeric + literals = abomination

[so]

On Sat, 27 Mar 2010 13:32:24 +0200, Robert Clipsham  
<robert at octarineparrot.com> wrote:

> On 27/03/10 10:20, so wrote:
>> In C++!
>>
>> I have a type defined in the core library like..
>> typedef float scalar;
>> //typedef double scalar; // <-- whole framework is now double precision
>
> alias float scalar;
> //alias double scalar;
>
>>
>> Next i instantiate vectors, matrices etc... from templates.
>> typedef vector_t<scalar, 3> vector;
>> typedef matrix_t<scalar, 3, 3> matrix;
>
> alias Vector!(scalar, 3) vector; // Presuming you have defined
>                                   // the Vector!() template somewhere
> alias Matrix!(scalar, 3, 3) matrix; // Presuming Matrix!() is defined
>
>> Until now everything cool, here pain comes...
>>
>> const scalar a = scalar(0.2) * math::consts<scalar>::pi; // can't drop
>> cast, since 0.2 is double
>
> const scalar a = 0.2 * PI; // PI is defined in std.math
>
>> const scalar b = a * scalar(0.9) + scalar(5); // " "
>
> const scalar b = a * 0.9 * 5.0;
>
>> const vector v = vector(8.0) * scalar(3.0); // can't drop cast, error
>
> const vector v = vector(8.0) * 3.0;
>
>> ...
>>
>> Since D is superb, i like to know how you do it in D.
>> If you got a better idea in C++, i would like to hear that too!
>>
>> Thanks!
>>
>
> There are a few vector implementations for D out there, or you can roll  
> your own. I'm pretty sure there's matrices out there too, I haven't  
> checked though (I'm pretty sure D's built in arrays will do the trick,  
> I'm not an expert though).

Even the example looks/sounds simple, i am not that new in C++/D  
programming :)
If one comes to D from C++, he is most likely pushing limits of the C++  
templates/numerics.
PI was just an example, i could find another constant, but then you would  
point me to a SI unit implementation. :)

For :
const scalar a = 0.2 * PI; // both double implicit cast to scalar, when it  
is float, this must produce a warning?
const scalar b = a * 0.9 * 5.0; // same
const vector v = vector(8.0) * 3.0; // 3.0 is a double, when scalar is  
float, this line must not compile

I think you should try it first, DMD should also give warnings/errors here.

Thanks!

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