Constructors: Member Initialization¶

Member Initialization? Assignment?¶

Initialization is different from assignment
Sometimes objects may not be left uninitialized
Sometimes objects/classes might not have a default constructor

class point
{
public:
    point(int x, int y)
    {
                                    // <--- space allocated for _x and _y, but value undefined
        _x = x;                     // <--- assignment
        _y = y;                     // <--- assignment
    }
private:
    int _x;
    int _y;
};

Real Initialization: Initializer List ¶

Not necessary with class point
⟶ Members have defined value after constructor has run (which is sufficient)
Good style though: use initializer list

class point
{
public:
    point(int x, int y)
    : _x(x), _y(y)                  // <--- real initialization
    {}                              // <--- body can be left empty
private:
    int _x;
    int _y;
};

Why Is That Important?¶

Hypothetical design decision …
- point objects can only be initialized
- Cannot be modified afterwards

class point
{
public:
    point(int x, int y)
    {
        _x = x;                        // <--- error: assignment of read-only member ‘point::_x’
        _y = y;                        // <--- error: assignment of read-only member ‘point::_y’
    }
private:
    const int _x;                      // <--- const!
    const int _y;                      // <--- const!
};

Why Else Is That Important?¶

Members might not have a default constructor
⟶ Cannot be left uninitialized - not even for a short time period