Re: Ada Annoyances

[Maciej Sobczak <see.my.homepage@gmail.com>]

> The example must demonstrate dispatch to the operation of the object's 
> type (the ultimate type) from a body defined for the parent type T class.

More complete demonstration:

#include <cstdio>

class Base
{
public:
    Base();
    
    virtual void vfoo();
};

class Derived : public Base
{
public:
    Derived();
    
    virtual void vfoo();
};

void useObject(Base & b)
{
    b.vfoo();
}

Base::Base()
{
    std::puts("   calling useObject from Base constructor:");
    
    useObject(*this);
}

void Base::vfoo()
{
    std::puts("      Hello from Base object!");
}

Derived::Derived()
{
    std::puts("   calling useObject from Derived constructor:");
    
    useObject(*this);
}

void Derived::vfoo()
{
    std::puts("      Hello from Derived object!");
}

int main()
{
    std::puts("test with Base object:");
    Base b;
    
    std::puts("");
    
    std::puts("test with Derived object:");
    Derived d;
}

$ g++ test.cpp
$ ./a.exe
test with Base object:
   calling useObject from Base constructor:
      Hello from Base object!

test with Derived object:
   calling useObject from Base constructor:
      Hello from Base object!
   calling useObject from Derived constructor:
      Hello from Derived object!

Since the Derived object is constructed in a two-step process, the useObject function is called twice, once from the Base part and once from the Derived part. The dispatch from the first call does not reach the not-yet-created parts of the object, which is a safe behavior.

> > C++ has stronger type safety than Ada in this particular context.
> 
> It is apples and oranges.

If you choose so. In this particular context, apples taste better.

> As I explained C++ has type-specific 
> constructors while Ada's Initialization is a class-wide constructor. You 
> cannot compare them.

I can and I should, since both are used to achieve the same design-level intent, which is construction of a newly created object.

-- 
Maciej Sobczak * http://www.inspirel.com