WeaponList.cpp

class Weapon {
public:
    virtual bool usable() const = 0;
    virtual double attack() = 0;
};

class Sword : public Weapon {
private:
    constexpr static auto startRatio = 0.2;
    constexpr static auto wearRatio = 0.8;
    double attackValue;
public:
    explicit Sword(double ownerAttack)
            : attackValue(startRatio * ownerAttack) {}
    bool usable() const override { return attackValue > 0; }
    double attack() override {
        auto ret = attackValue;
        attackValue *= wearRatio;
        return ret;
    }
};

class Arrow : public Weapon {
private:
    int remaining = 3;
public:
    static double attackValue;
    Arrow() = default;
    Arrow(double) {}
    bool usable() const override { return remaining > 0; }
    double attack() override {
        if (!usable()) { return 0; }
        --remaining;
        return attackValue;
    }
};
double Arrow::attackValue;

class Bomb : public Weapon {
public:
    Bomb() = default;
    Bomb(double) {}
    bool usable() const override { return true; }
    double attack() override { return -1; }
};

template<typename T>
Weapon *make(double param = 0) {
    return new T{param};
}

using WeaponPtr = Weapon*;
using WeaponCreator = WeaponPtr(*)(double);
WeaponCreator WeaponList[] = {make<Sword>, make<Arrow>, make<Bomb>};