Re: allocating an object of abstract class type error

Posted by Yannis on Jan 17, 2017; 4:32pm
URL: http://quantlib.414.s1.nabble.com/allocating-an-object-of-abstract-class-type-error-tp17968p17972.html

It is definitely possible using C++ metaprogramming.

One strategy could be to process all classes T regardless of whether each particular class T is abstract or not.

Then rather than calling new T(arg), where arg is some argument, you should call New<T>::Res::f(arg)

Above New<T> is a template class that you must define in such a way that it contains a typedef called Res, which in turn is designed to equal one of the following two classes: NewDoNothing or NewDoSomething<T>.

The first class NewDoNothing must contain a static method f that does nothing.

The second class NewDoSomething<T>, which is a template, must contain a static method also called f that returns new T(arg).

The idea is that New<T>::Res intelligently switches between NewDoNothing and NewDoSomething<T> based upon whether T is abstract or not.

This intelligent switch can be easily implemented for a generic argument arg, as long as it is a single argument.

I suppose this method can be generalized for any number of arguments, including the case of no arguments at all.

Let me know if this is an approach you would like to follow and I could send you some code that I have that implements this switch.

Regards,

Ioannis

Luigi Ballabio <[hidden email]> schrieb am 14:07 Donnerstag, 12.Januar 2017:

No, I don't think there is.

On Thu, Jan 12, 2017 at 2:02 PM Jerry Jin <[hidden email]> wrote:

Hi Luigi

Thanks, is there any tool or document to identify which class is abstract that I can use new to allocate memory?

I'm working a wrapper program, which iterate all classes, hence it would be great to know which classes I can't do 'new' before compiling

Regards

Jerry

On Thu, Jan 12, 2017 at 7:33 PM, Luigi Ballabio <[hidden email]> wrote:

A class is abstract when it (or one of its base classes) declares a pure virtual method and doesn't define it.

In your case: CmsSpreadCouponPricer inherits from FloatingRateCouponPricer, which declares a bunch of virtual methods:

        virtual Real swapletPrice() const = 0;

        virtual Rate swapletRate() const = 0;

        virtual Real capletPrice(Rate effectiveCap) const = 0;

        virtual Rate capletRate(Rate effectiveCap) const = 0;

        virtual Real floorletPrice(Rate effectiveFloor) const = 0;

        virtual Rate floorletRate(Rate effectiveFloor) const = 0;

        virtual void initialize(const FloatingRateCoupon& coupon) = 0;

so FloatingRateCouponPricer is abstract. CmsSpreadCouponPricer doesn't define them, so it's also abstract. LognormalCmsSpreadPricer inherits from CmsSpreadCouponPricer and defines them (that is, gives them actual bodies) so it's a concrete class and can be instantiated.

For more details, you can probably check any C++ book.

Cheers,

    Luigi

On Thu, Jan 12, 2017 at 4:52 AM Jerry Jin <[hidden email]> wrote:

Hello, QuantLib community

I'm getting error 'allocating an object of abstract class type error' sometimes while working with some classes

For example:

return new CmsSpreadCouponPricer(correlation);

How do I know which class is abstract and can't allocate memory?

Thanks!

Regards

Jerry

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