C# Vector Class – Interpolation Design Decision

cclass-designdesignextension-methodobject-oriented

Currently I'm coding a Vector class in C# and I'm coming to the point, where I've to figure out, how I want to implement a function/method to interpolate between two vectors. The (obvious) and also my first solution was to simply implement it as a method in the vector class itself:

public class Vector3D
{
    public static Vector3D LinearInterpolate(Vector3D vector1,
        Vector3D vector2, double factor) { ... }

    public Vector3D LinearInterpolate(Vector3D other, double factor { ... }
}

(I decided to offer both a static method with two vectors as parameters and one non-static, with only one vector as the parameter)

But then I got the idea to use extension methods (defined in a separate class called e.g. Interpolation for example), since interpolation isn't really limited to vectors only. So this might be another approach:

public class Vector3D { ... }

public static class Interpolation
{
    public static Vector3D LinearInterpolate(this Vector3D vector,
        Vector3D other, double factor) { ... }
}

And here is an example showing how one would use the different implementations:

{
    var vec1 = new Vector3D(5, 3, 1);
    var vec2 = new Vector3D(4, 2, 0);
    Vector3D vec3;

    vec3 = vec1.LinearInterpolate(vec2, 0.5); //1
    vec3 = Vector3D.LinearInterpolate(vec1, vec2, 0.5); //2

    //or with extension-methods

    vec3 = vec1.LinearInterpolate(vec2, 0.5); //3 (same as 1)
    vec3 = Interpolation.LinearInterpolation(vec1, vec2,
    0.5); //4
}

I can't really decide on which design is preferable. Is there a rule of thumb on how to implement methods/functions similar to the one above or is it rather a matter of preference? I really would like to hear your opinions on what's better and – if possible – why.

Best Answer

Maybe it is that I come from Java, but I really don't like extension methods unless there is a good reason for it.

If you want to reuse the operation code, the solution should be composition. Create an Interpolator that operates over an IEnumerable<double> (unluckily, it seems that C# lacks an equivalent to java.lang.Number, so you can't make the class generic easily). I don't think it is a bad idea that your Vector class implements it, too.

For bonus points, make the class an interface that defines the operation and inject an instance of the interface in the object, so you can change the implementation (or even use other types of interpolations, if they match the method signature) at will.

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