Re: Delegation question...

From:

=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?= <Erik-wikstrom@telia.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 24 May 2008 07:37:31 GMT

Message-ID:

<%APZj.7547$R_4.6308@newsb.telia.net>

On 2008-05-23 23:58, barcaroller wrote:

What is the common way/design-pattern (if any) in C++ for delegating
function calls that are not handled by a certain class. Public
inheritance would be one way but not all classes are meant to inherit
from (e.g. STL).

Example:

    class A
    {
        public:
            foo();

        private:
            set<string> myset;
    }

    A myObj;
    myObj.insert(); // compiler error of course

Is there some mechanism (direct or indirect) where a function that is
not handled by myObj gets delegated to another object (e.g. myset)?

Private inheritance is one way to do it:

#include <iostream>

class Foo
{
public:
  void print() { std::cout << "Foo\n"; }
};

class Bar : private Foo
{
public:
  using Foo::print;
};

int main()
{
  Bar b;
  b.print();
}

But most often I would recommend to manually do the delegation:

#include <iostream>

class Foo
{
public:
  void print() { std::cout << "Foo\n"; }
};

class Bar
{
  Foo f;
public:
  void print() { f.print(); }
};

int main()
{
  Bar b;
  b.print();
}

--
Erik Wikstr??m