Vector of Abstract Classes in C : A Primer
In C , abstract classes provide a way to define interfaces without implementation, allowing derived classes to inherit and implement specific behaviors. However, unlike in C#, where interfaces can be instantiated directly, abstract classes in C cannot be.
The Problem
Consider the following C example:
class IFunnyInterface { public: virtual void IamFunny() = 0; };
This abstract class represents an interface with a single method, IamFunny. Now, let's say we want to create a vector of objects that implement this interface, such as:
std::vector<ifunnyinterface> funnyItems;</ifunnyinterface>
This code will result in the following compiler error:
error C2259: 'IFunnyInterface' : cannot instantiate abstract class
This error occurs because C does not allow instantiation of abstract classes.
A Workaround
One workaround is to replace the abstract class with a concrete class that throws an exception when attempting to call an unimplemented method:
class IFunnyInterface { public: virtual void IamFunny() { throw new std::exception("not implemented"); } };
While this workaround allows the vector instantiation, it introduces a potential pitfall: code that attempts to access the methods of an IFunnyInterface object will need to handle the exception.
An Alternative Solution
A more elegant solution is to use a vector of pointers to abstract classes:
std::vector<ifunnyinterface> ifVec;</ifunnyinterface>
This approach allows for polymorphic behavior and avoids the object slicing problem that can occur with direct value storage.
By understanding the limitations of abstract class instantiation in C , you can employ appropriate workarounds or use alternatives to achieve the desired functionality in your code.
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