Technical Stuff

Example for changing constant object data member:

class mute{
public:
int x ;
mutable int y; // mutable variable declaration
mute() // constructor
{
x=10;
y=10;
}
};
int main()
{
const mute m; // constant object
//m.x=20; // Illegal cant change the data members in a constant object
m.y=20; // Legal, we can change , because its a mutable
}

For the above sampel code, there is class mute with one int and one mutable int data member functions. There is constant object for the class. If you try to modify the normal data members here it is x in line no.16, we will get compilation error. But we can modify the mutable data , here it is y in line no.17.

Example for changing the constant function data:

class mute{
public:
int x ;
mutable int y;
mute()
{
x=10;
y=10;
}
void setValue(int a) const
{
//x=a; // Illegal, cant change the values in constant function
y=a; // legal, mutable data allowed to change in constant functions
}
};
int main()
{
mute m;
m.setValue(5);
}