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Re: New feature in C++ wanted: friend limited to one function only in a class

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On 8/25/2022 7:11 PM, JiiPee wrote:
> I had this situation many times, that I wanted to use friend in class 
> but I dont want friend be able to get
> access to ALL members, only maybe one function. I wish there was a 
> feature in C++ like this:
> 
> class Parent
> {
> private:
>      void foo() { : friend Child // new feature
>      }
> 
>      void foo2() {
>      }
> };
> 
> and now Child can get access to foo() and ONLY it:
> 
> class Child
> {
> public:
>      Parent* m_parent{nullptr}; // later initialized ...
>      void foo3() {
>          // Can access only foo()
>          m_parent->foo(); // this is OK
>          // cannot access any other privates
>          m_parent->foo2(); // this is NOT OK
>      }
> };
> 
> Can anybody suggest this to Bjarne? hehe

I don't think this would be a good idea ("selective" friendship, not 
contacting Bjarne..)
- friend by itself should be used parsimoniously: it goes against 
encapsulation, so more often than not it is a symptom of poor design 
(exceptions apply, but they are in fact exceptions)
- "selective" friendship, in the way you are suggesting, breaks 
encapsulation even more, in that it introduces a new level of its 
fragmentation.

Others have given solutions that do what you are trying to do.
If I had to address this issue, I'd look for a different and possibly 
more consistent design, e.g. simply:

class Parent_public
{
public:
   void foo();
};

class Parent : public Parent_public
{
private:
   void foo2();
};

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New feature in C++ wanted: friend limited to one function only in a class JiiPee <kerrttuPoistaTama11@gmail.com> - 2022-08-25 20:11 +0300
  Re: New feature in C++ wanted: friend limited to one function only in a class "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-08-25 20:13 +0200
    Re: New feature in C++ wanted: friend limited to one function only in a class JiiPee <kerrttuPoistaTama11@gmail.com> - 2022-08-25 23:13 +0300
  Re: New feature in C++ wanted: friend limited to one function only in a class JiiPee <kerrttuPoistaTama11@gmail.com> - 2022-08-25 23:11 +0300
  Re: New feature in C++ wanted: friend limited to one function only in a class Manfred <noname@add.invalid> - 2022-08-26 01:59 +0200
    Re: New feature in C++ wanted: friend limited to one function only in a class JiiPee <kerrttuPoistaTama11@gmail.com> - 2022-08-26 07:19 +0300
    Re: New feature in C++ wanted: friend limited to one function only in a class JiiPee <kerrttuPoistaTama11@gmail.com> - 2022-08-26 07:25 +0300
  Re: New feature in C++ wanted: friend limited to one function only in a class Paavo Helde <eesnimi@osa.pri.ee> - 2022-08-26 12:13 +0300
    Re: New feature in C++ wanted: friend limited to one function only in a class JiiPee <kerrttuPoistaTama11@gmail.com> - 2022-08-26 19:29 +0300
      Re: New feature in C++ wanted: friend limited to one function only in a class Paavo Helde <eesnimi@osa.pri.ee> - 2022-08-26 20:49 +0300
  Re: New feature in C++ wanted: friend limited to one function only in a class Michael S <already5chosen@yahoo.com> - 2022-08-26 03:55 -0700

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