import std;

​

struct Point4 {

  union {

    float[4] cs = [1,2,3,4];

    struct { float x,y,z,w; }

  }

  float opIndex( size_t i)

    in( i <= 3) // unsigned never become <0

  {

    return cs[ i];

  }

  void opIndexAssign( float v, size_t i)

    in( i <= 3)

  {

    cs[ i] = v;

  }

}

​

// check for no UB

static assert( Point4.sizeof == 16 );

​

void main() {

    Point4 p;

    p[2].writeln;

    assert( p[2] == p.z );

    p[5] = 0;

}