Sometimes I find myself writing comments on class methods like this:

class A : public Base
{
public:
    /**
      * Sets variable;
      * should be called before ImplementsInterfaceMtehod(),
      * else has no effect.
      */
  void SetSomeVariable( var_type value );

  virtual void ImplementsInterfaceMethod();
}

The callers of Base::ImplementsInterfaceMethod obviously do not know about the variable, and should not. But the users of A should set the variable if they want it to take effect. It is not required to set the variable (else it could be a parameter for the constructor), so I cannot throw exceptions in ImplementsInterfaceMethod if it is not set.

Is this a sign of some typical bad practice? Is there a better way than writing a comment as shown to deal with this?