Philosophical reason behind the concept of friend function

[Madhav]

Hi all,
I am a newbie in c++. I want to know what is the
philosophical reason behind the existence of friend functions. I
thought giving access to private data to a function which is not a
member of the class is a violation of encapsulation.

Thanks,
Madhav.

 

[Aleksander Beluga]

Hi all,
I am a newbie in c++. I want to know what is the
philosophical reason behind the existence of friend functions. I
thought giving access to private data to a function which is not a
member of the class is a violation of encapsulation.

Thanks,
Madhav.

Unfortunately, we're not living in an ideal world. That means that
sometimes (like when building singleton holder or some generic
framework) it's OK to access one's private properties. And, yeah,
sometimes (hey, I said SOMETIMES, don't kill me!) it is even appropriate
to use goto )

 

[GB]

Hi all,
I am a newbie in c++. I want to know what is the
philosophical reason behind the existence of friend functions. I
thought giving access to private data to a function which is not a
member of the class is a violation of encapsulation.

Thanks,
Madhav.

It is only giving access to *arbitrary* functions (e.g., by making data
public) that is a violation of encapsulation. Having the class identify
a *specific* function for access is not a violation of encapsulation,
since the class is giving that access. The function becomes part of the
encapsulation along with the member functions. That said, it should be
rare that non-members need such access.

Gregg

 

[benben]

Hi all,
I am a newbie in c++. I want to know what is the
philosophical reason behind the existence of friend functions. I
thought giving access to private data to a function which is not a
member of the class is a violation of encapsulation.

Thanks,
Madhav.

The philosophical reason: to extend encapsulation boundary over that
defined by the class.

Ask yourself what is being encapsulated from whom

Regards,
Ben

 

[Jerry Coffin]

@i39g2000cwa.googlegroups.com>, (e-mail address removed)
says...

Hi all,
I am a newbie in c++. I want to know what is the
philosophical reason behind the existence of friend functions. I
thought giving access to private data to a function which is not a
member of the class is a violation of encapsulation.

The reason is pretty simple: sometimes functions that are
part of the interface to a class can't actually be member
functions. When this happens, the non-member function is
normally made a friend of the class.