Two predicated methods. -- ADTmag

Two predicated methods.

By David Maley, Ivor Spence
August 1, 2001

Supporting Design by Contract in C++
by David Maley and Ivor Spence
Listing 1. Two predicated methods.


Complex Complex::operator/(const double& d)
{
  if (!Invariant())
    throw BadComplex(*this);
  if (d==0)
    throw DivideByZero();
  Complex old(*this);
  Complex result = // code;
  if (result*d!=old)
    throw BadComplexDivide(*this);
  if (!Invariant())
    throw BadComplex(*this);
  return result;
}

T Stack<T>::pop()
{
  if (!Invariant())
    throw BadStack<T>(*this);
  if (count()<=0)
    throw EmptyStack();
  Stack old(*this);
  T result = // code;
  if (result!=old.top() || count()!=old.count()-1)
    throw BadPop(*this);
  if (!Invariant())
    throw BadStack<T>(*this);
  return result;
}

About the Authors

David Maley is with St. Mary's University College, Belfast. He can be contacted at [email protected].

Ivor Spence is with Queen's University of Belfast. He can be contacted at [email protected].