Class templates

[Nirklas]

I'm having some trouble getting my new, fancy, templated Interpolator class compiling. The problem is that I'm not as comfortable with the template-syntax as I ought to be. Lots of respect and gratitudes to anyone who can help me identify my mistakes.

class Interpolator
{
	Interpolator()
	{}

public:
	virtual ~Interpolator()
	{
	}

	virtual void Reset() = 0;
	virtual void Interpolate(float timespan) = 0;
};

template<typename T>
class InterpolatorImpl : public Interpolator
{
public:
	typedef typename T ValueType;

private:
	struct Keyframe
	{
		InterpolatorImpl<T>::ValueType value_;
		float time_;
	};

	typedef std::list<InterpolatorImpl<T>::Keyframe> KeyframeList;

public:
	InterpolatorImpl() : currentTime_(0), pTarget_(0)
	{
	}

	virtual ~InterpolatorImpl()
	{
	}

	void SetTarget(ValueType* pTarget)
	{
		pTarget_ = pTarget;
	}

	void AddKeyframe(const ValueType& value_, float time);

	virtual void Interpolate(float timespan);

	virtual void Reset()
	{
		currentTime_ = 0;
	}

private:
	float		currentTime_;
	KeyfameList	keyframes_;

	ValueType*	pTarget_;
};

//Usage
int main()
{
	float myFloat = 0;
	InterpolatorImpl<float>* myInterp = new InterpolatorImpl<float>();
	myInterp->AddKeyframe(24.5f, 2);
	myInterp->AddKeyframe(0, 5);
	myInterp->SetTarget(&myFloat);

	float timespan = 0.05f;
	for(float t=0; t<6; t+=timespan)
	{
		myInterp->Interpolate(timespan);
		cout << myFloat << endl;
	}

	delete myInterp;
}

The compliler complains about "error C2501: 'InterpolatorImpl<T>::Keyframe::value_' : missing storage-class or type specifiers" amongst other things, but that seems to be the root of all the evil...

any ideas?

/Niklas Andersson
Sweden

[wien]

Basically, there are a lot of little mistakes in your code. I won't go into the details here (unless you want me to), but I fixed up your code so you can take a look at it youself.

#include <list>
#include <iostream>

class Interpolator
{
protected:
	Interpolator()
	{}

public:
	virtual ~Interpolator()
	{
	}

	virtual void Reset() = 0;
	virtual void Interpolate(float timespan) = 0;
};

template<typename T>
class InterpolatorImpl : public Interpolator
{
public:
	typedef T ValueType;

private:
	struct Keyframe
	{
		typename InterpolatorImpl<T>::ValueType value_;
		float time_;
	};

	typedef std::list<Keyframe> KeyframeList;

public:
	InterpolatorImpl() : currentTime_(0), pTarget_(0)
	{
	}

	virtual ~InterpolatorImpl()
	{
	}

	void SetTarget(ValueType* pTarget)
	{
		pTarget_ = pTarget;
	}

	void AddKeyframe(const ValueType& value_, float time);

	virtual void Interpolate(float timespan);

	virtual void Reset()
	{
		currentTime_ = 0;
	}

private:
	float		currentTime_;
	KeyframeList	keyframes_;

	ValueType*	pTarget_;
};

//Usage
int main()
{
	float myFloat = 0;
	InterpolatorImpl<float>* myInterp = new InterpolatorImpl<float>();
	myInterp->AddKeyframe(24.5f, 2);
	myInterp->AddKeyframe(0, 5);
	myInterp->SetTarget(&myFloat);

	float timespan = 0.05f;
	for(float t=0; t<6; t+=timespan)
	{
		myInterp->Interpolate(timespan);
		std::cout << myFloat << std::endl;
	}

	delete myInterp;
}

This code compiles fine, but does not link as it's missing a couple of function definitions.

[Nirklas]

Wohoo! Swell!
No, you don't have to go into details. It was the use of "typename" that was the main problem, and the answer i needed.
You've been very helpful today =) Thanks alot!

/Niklas