How to use a member variable as a default argument in C++?

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Default argument expressions for a member function can only depend on things that are in class or global scope. The default argument also has to be specified in the method’s declaration (i.e. in the header file).

To get around this, you need 2 overloads of your MoveTo method. One that takes 1 argument, and another that takes 2 arguments. The method taking 1 argument calls the other method, passing along the value that you consider as the default.

void Object::MoveTo(double speed)
{
    MoveTo(speed, initPos);
}

void Object::MoveTo(double speed, Point position)
{
    // Everything is done here.
}

Note that when you make MoveTo(double) call MoveTo(double, Point), it allows you to write the implementation of MoveTo only once, thereby respecting the DRY principle.

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