Create objects by passing different parameters

Question

I have a class hierarchy of interpolators like this:

class BaseInterpolator
{
public:
    virtual ~BaseInterpolator();

    virtual float GetInterpolation(const float input) const = 0;
};

class AccelerateInterpolator : public BaseInterpolator
{
public:
    explicit AccelerateInterpolator(const float factor = 1.0f);
    virtual float GetInterpolation(const float input) const override;
private:
    float m_factor;
};

class AnticipateOvershootInterpolator : public BaseInterpolator
{
public:
    explicit AnticipateOvershootInterpolator(const float tension = 2.0f, const float extraTension = 1.5f);
    virtual float GetInterpolation(const float input) const override;
private:
    float m_tension;
    float m_extraTension;
};

I would like to be able to construct these objects with different parameters. However, there is different number of parameters for each possible derived type from BaseInterpolator, i.e AccelerateInterpolator has 1, AnticipateOvershootInterpolator has 2. I have also class abstracting properties which client passes to my library which creates Interpolators based of those properties:

struct AnimationProperties
{
    enum class Curve
    {
        Accelerate,
        AnticipateOvershoot,
    };

    Curve curve;
    uint32_t duration{ 0 };
};

I would like to add possibility to user to pass different params via AnimationProperties, so I can create parametrized Interpolator using those params. Until now I've used unparametrized interpolators. I'm not sure how I should approach this. Should I use visitor somehow, or what is the correct approach?

Btw. User only sees AnimationProperties

Possible duplicate: Create objects by passing different parameter in c++? — Thomas Matthews
– Thomas Matthews, Commented Apr 3, 2018 at 18:11
Can you get together with your classmate, Ahmed Shahin and with your instructor. You instructor needs to be informed of topics that were not communicated well. — Thomas Matthews
– Thomas Matthews, Commented Apr 3, 2018 at 18:15

PiotrNycz · Accepted Answer · 2018-04-03 16:55:22Z

2

You need Factory Design Pattern - or even Abstract Factory.

Keeping your naming scheme - it should look like following:

class BaseInterpolatorFactory
{
public:
    virtual ~BaseInterpolatorFactory() = default;
    virtual std::unique_ptr<BaseInterpolator> CreateObject() = 0;
};

E.g. implementation for AnticipateOvershootInterpolator:

class AnticipateOvershootInterpolatorFactory : public BaseInterpolatorFactory
{
public:
    AnticipateOvershootInterpolatorFactory (float tension, float extraTension);
    std::unique_ptr<BaseInterpolator> CreateObject() override
    {
         return std::make_unique<>(m_tension, m_extraTension);
    }
private:
    float m_tension;
    float m_extraTension;
};

So - in client code, instead of passing some combined struct/union/discriminator of parameters - just pass BaseInterpolatorFactory&

answered Apr 3, 2018 at 16:55

PiotrNycz

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