Know your design tools — The Performing Half-baked object case

Among other important paradigms in software design, object orientation is a common set of design techniques these days. Hierarchies of classes, derivative class instantiations and virtual calls can be often found on software codebases. Hence, the relevance of the Performing Half-baked object case while designing object-oriented software.

The Performing Half-baked object case occurs where a virtual call is executed onto an unborn or uncreated or uninitialized class instance: the actual behavior can be unexpected, of course.

A couple of examples.

Consider the output of this Windows/Visual C++ code:

#include <iostream>

class AA
{
    public:
    AA()
    {
        std::cout << "AA()\n";
        f();
    }
    virtual void f() { std::cout << "AA.f\n"; }
};

class BB : public AA
{
    public:
    BB()
    {
        std::cout << "BB()\n";
        f();
    }
    virtual void f() { std::cout << "BB.f\n";}
};

void main()
{
	auto x = new BB;
}

For another –different– behavior, consider the output of this .NET/Visual C^# code:

using static System.Console;

class AA
{
    public AA()
    {
        WriteLine("AA()");
        f();
    }
    public virtual void f() => WriteLine("AA.f");
}

class BB : AA
{
    public BB()
    {
        WriteLine("BB()");
        f();
    }
    public override void f() => WriteLine("BB.f");
}

class Program
{
    public static void Main()
    {
        var x = new BB();
    }
}

The Performing Half-baked object is a case that designers of object-oriented languages and runtimes have typically faced. Any designer using those languages and runtimes should be aware of this and other cases during the process of object creation.