如何使用类成员函数作为默认值

Question

I have this class

class InventoryManagement
{
public:
    typedef void(InventoryManagement::*Action)(void);
    typedef void(InventoryManagement::*ActionWithReturn)(InventoryItem);

    void Initialize(int inventoryQty, int maxQty, ActionWithReturn onAdd = nullptr , Action onMaxQtyReach = nullptr, Action onQtyReset = nullptr, Action onSideChnage = nullptr);

    Action getStrategyOnMaxQtyReach();
    Action getStrategyOnQtyReset();
    Action getStrategyOnSideChange();
    ActionWithReturn getOnAdd();

private:

    // Private Functions Data members
    ActionWithReturn m_onAdd;
    Action m_OnSideChange;
    Action m_OnQtyReset;
    Action m_OnMaxQtyReach;


    // Default Function 
    void OnAddDefault(InventoryItem item) { }
    void OnMaxQtyReachDefault() { }
    void OnQtyResetDefault() { }
    void OnSideChangeDefault() { }
};

The function Initialize sets the data members of type Action . I created default actions that do noting and I want to pass them as default arguments. If the user doesn't send any function pointer to Initialize then those functions will be set.

The signature of the function is:

void Initialize(int inventoryQty, int maxQty, ActionWithReturn onAdd = nullptr , Action onMaxQtyReach = nullptr, Action onQtyReset = nullptr, Action onSideChnage = nullptr);

I tried void Initialize(int inventoryQty, int maxQty, ActionWithReturn onAdd = InventoryManagement::OnAddDefault , Action onMaxQtyReach = nullptr, Action onQtyReset = nullptr, Action onSideChnage = nullptr); instead of nullptr , but the compiler emitted "Call to non-static member function without an object argument" .

Answer 1

The syntax is &InventoryManagement::OnAddDefault :

void Initialize(
    int inventoryQty,
    int maxQty,
    ActionWithReturn onAdd = &InventoryManagement::OnAddDefault, // <-- 
    Action onMaxQtyReach = nullptr,
    //... etc
)

On a side node, I encourage you to consider using constructors instead of initialize methods.