c++ and IoC

From:
Vladimir Jovic <vladaspams@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Tue, 03 Aug 2010 10:33:35 +0200
Message-ID:
<i38k90$ofk$1@news.albasani.net>
Hello,

Following this :
http://www.codinginlondon.com/2009/05/cheap-ioc-in-native-c.html
I implemented an example of how I see IoC. This is just a naive attempt,
since the way the parameters are passed to the constructor is not very
good (at least in my opinion :) )

Can someone recommend a better way? A link to an example, or explanation
how it is done, would be best.

Here goes long example :

/// CODE
#include <string>
#include <map>
#include <iostream>
#include <typeinfo>
#include <cassert>
#include <memory>

class I
{
     public:
         I()
         {
         }
         virtual ~I()
         {
         }

         void foo()
         {
             doFoo();
         }

     private:
         virtual void doFoo() = 0;
};

class A : public I
{
     public:
         A( const int v_) : I(),
                            v( v_ )
         {
             std::cout<<"A::A() v="<<v<<std::endl;
         }
         virtual ~A()
         {
             std::cout<<"A::~A()"<<std::endl;
         }

         static void setParams( const int nextParam )
         {
             newCreateParam = nextParam;
         }
         static I* create()
         {
             return new A( newCreateParam );
         }

     private:
         virtual void doFoo()
         {
             std::cout<<"A::doFoo() v="<<v<<std::endl;
         }

         int v;

         static int newCreateParam;
};
int A::newCreateParam=0;

class B : public I
{
     public:
         B() : I()
         {
             std::cout<<"B::B()"<<std::endl;
         }
         virtual ~B()
         {
             std::cout<<"B::~B()"<<std::endl;
         }

         static I* create()
         {
             return new B;
         }

     private:
         virtual void doFoo()
         {
             std::cout<<"B::doFoo()"<<std::endl;
         }
};

std::map< std::string, I* (*)() > GetCreator()
{
     std::map< std::string, I* (*)() > m;

     m[ typeid(A).name() ] = &A::create;
     m[ typeid(B).name() ] = &B::create;

     return m;
}
const std::map< std::string, I* (*)() > creator = GetCreator();

I* CreateObj( const std::string whichOne )
{
     std::cout<<"Creating new object of type = " << whichOne << std::endl;

     for ( std::map< std::string, I* (*)() >::const_iterator it =
creator.begin(); creator.end() != it; ++ it )
     {
         if ( std::string::npos != it->first.find( whichOne ) )
         {
             I* (*func)() = it->second;
             return func();
         }
     }

     std::cout<<"The creator for the class " << whichOne << " not
found." << std::endl;

     return NULL;
}

int main()
{
     A::setParams( 55 );

     std::auto_ptr< I > newObj1( CreateObj( "B" ) );
     std::auto_ptr< I > newObj2( CreateObj( "A" ) );
     std::auto_ptr< I > newObj3( CreateObj( "C" ) );

     if ( NULL != newObj1.get() )
     {
         newObj1->foo();
     }
     if ( NULL != newObj2.get() )
     {
         newObj2->foo();
     }
     if ( NULL != newObj3.get() )
     {
         newObj3->foo();
     }
}

/// END OF CODE

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