Question

I’m playing with the default arguments for my Settings class in my project, so that I have a bit fewer methods declared.

For instance, I have these methods declared:

class Settings
{
    // [..]

    int getCurrentUserID(); // returns current user id

    // you specify the user id
    int setSetting( int value, int user_id ); 
    // no user specified, use the current one, overloads the previous when called
    // with only 1 argument
    int setSetting( int value ); 
}

What I’d like to have is this simplified version:

class Settings
{
    // [..]

    int getCurrentUserID(); // returns current user id

    // automatically selects the current user if no ID is provided
    int setSetting( int value, int user_id = getCurrentUserID() ); 
}

But I get this error at compilation:

cannot call member function ‘int Settings::getCurrentUserID()’ without object

How could I tell the compiler to use the current instance (which is available through the this) of the Setting object to get the default value?
Is this authorized, by the way?

Answer 1

The method getCurrentUserID() is not static, so you can only call it through an object. One option is to create 2 methods, like the ones bellow, this and call the one you need:

int setSetting(int value);

int setSetting(int value, int user_id);

Another option: assuming the ID is always positive, you can give a default negative ID on the method and verify inside the method if the method was called with an ID or not. Something like this:

int setSetting(int value, int user_id = -1) {
    if (user_id == -1) {
        this->setSetting(value, this.getCurrentUserID());
        return 0; //don't know what the function returns, but handle it the way you need
    }

    // rest of the function will be called recursively, but it's OK
    // because the ID is not -1!
}