/+dub.sdl:

dependency "sumtype" version="~>0.4.1"

+/

​

import std.math: approxEqual, cos, PI, sqrt;

import sumtype;

​

struct Rectangular { double x, y; }

struct Polar { double r, theta; }

alias Vector = SumType!(Rectangular, Polar);

​

pure @safe @nogc nothrow

double length(Vector v)

{

    return v.match!(

        rect => sqrt(rect.x^^2 + rect.y^^2),

        polar => polar.r

    );

}

​

pure @safe @nogc nothrow

double horiz(Vector v)

{

    return v.match!(

        rect => rect.x,

        polar => polar.r * cos(polar.theta)

    );

}

​

void main()

{

    Vector u = Rectangular(1, 1);

    Vector v = Polar(1, PI/4);

​

    assert(length(u).approxEqual(sqrt(2.0)));

    assert(length(v).approxEqual(1));

    assert(horiz(u).approxEqual(1));

    assert(horiz(v).approxEqual(sqrt(0.5)));

}