length property
      
      set
      length
      (double value) 
      
    
    
Set the length of the vector. A negative value will change the vectors
orientation and a value of zero will set the vector to zero.
Implementation
set length(double value) {
  if (value == 0.0) {
    setZero();
  } else {
    var l = length;
    if (l == 0.0) {
      return;
    }
    l = value / l;
    _v2storage[1] *= l;
    _v2storage[0] *= l;
  }
}