IloGoals are not extractables and they are not added to the model. Instead, they are used directly by the instance of IloSolver. Goals are not extracted, even though there is a pseudo-extraction mechanism; the virtual method IlcGoal IloGoalI::extract(IloSolver) is called to create a corresponding IlcGoal.

The consequence of the fact that goals are not extractables is quite simple. A goal does not extract its subextractables. They must be extracted as a consequence of the extraction of the model.

For instance, the following code is incorrect:

IloEnv env;
IloIntVar x(env, 0, 10);
IloIntVar y(env, 0, 10);
IloIntVar z(env, 0, 10);
IloModel model(env);
model.add(x < y);
IloSolver solver(model);
solver.solver(IloInstantiate(env, z));

In the last line, the extraction of the IloInstantiate goal will raise an exception because z will not be extracted in the model. A simple way to ensure that this problem does not occur is to add subextractables directly to the model.

The following code is correct:

IloEnv env;
IloIntVar x(env, 0, 10);
IloIntVar y(env, 0, 10);
IloIntVar z(env, 0, 10);
IloModel model(env);
model.add(x < y);
model.add(z);
IloSolver solver(model);
solver.solver(IloInstantiate(env, z));