Is there a way to set an alias to specific form of a template?

[Ali Çehreli]

On Fri, 07 Oct 2011 18:29:26 -0700, Roderick Gibson wrote:

> This may be the completely wrong approach, but I am basically thinking
> of something like this (I am aware this will not compile, it's
> psuedocode):
> 
> class Vector(T) {
> 	... //definition here
> }
> 
> alias Vector(float, float) vec2f;
> auto v = new vec2f(1.0,1.0);
> 
> I am making a templated Vector class (a mathematical vector) that will
> have varying types (thus a template) and dimensions (via variadic
> functions), so that the same template definition will work for 2d or 3d
> vectors (or 4d, etc).
>
> I then want the programmer to be able to define
> the specific forms that he wants so he can easily keep track of them
> (without getting confused about which is a 2d integer vector and which
> is a 3d float vector), and then use those forms in a type safe manner.
> Is this even possible? If it is, but it's the wrong way to do it, what's
> the right way?
> 
> Basically I wanted to write it once and not worry about writing it again
> to handle different types and dimensions (no vec2i class, or vec2f, or
> vec3f, or vec3i, etc). Templates easily handles the type requirement,
> but what about the dimensional requirement? Am I just going to have to
> rewrite it when I add dimensions?

You can take advantage of 'Template Value Parameters' and 'Typesafe 
Variadic Functions':

  http://www.d-programming-language.org/
template.html#TemplateValueParameter

  http://www.d-programming-language.org/function.html

class Vector(T, int N)
{
    T[N] elements;

    this(T[] elements ...)
    {
        this.elements = elements;
    }
}

alias Vector!(double, 2) Vec2D;
alias Vector!(double, 3) Vec3D;

void main()
{
    auto v2d = new Vec2D(2.2, 2.2);
    auto v3d = new Vec3D(3.3, 3.3, 3.3);

    // Alternatively, all parameters at once:
    auto v3d_too = new Vec3D([ 33, 33, 33, ]);
}

(Some would find 'size_t N' to be more appropriate since N is a 
dimension.)

Ali