🚀 go-pugleaf

In article eos@mhost.ida.his.se, anders@ida.his.se (Anders Eklund) writes:
>
>Friends break the rules of encapsulation and should be avoided
>as much as possible, but sometimes they must be used anyway.
>When I have used friends they only had to use one or a
>few members of the class. As it is now all members are
>accessible to the friend. I would like to specify which members
>the friend can access. There is no way to do that today, but
>would it not be nice to be able to do so? Any comments?

I disagree with your premise. Friends can be used to violate
encapuslation, but so can the "public:" access specifier. A friend
function does not break encapsulation merely by existing. A friend
function must be declared with the class. The owner of the class
also owns the friend functions.

IMHO you should view a friend as part of the public interface. That
is, from a class design point of view, a friend function is equivalent
to a public static member function: it has no "this" pointer, but can
access the entire class.

The only significant difference is the syntax used to access the function.
For example, an overloaded operator+() as a static member function makes
little sense; you could not use the infix operator notation. As a non-static
member function it is asymetric and thus inconvenient to use. As a friend
function it is convenient to use with no surprises.

If it makes sense to provide a way to limit the access a friend function
has to a class, it must also make sense to limit the access of a member
function, yet nobody ever suggests the latter as a good idea.

It seems to me that fine-grained access control (e.g. function A can
access members x, y, and z; function B can access member x only; function
C can access y and z) would be cumbersome to use and would make maintenance
more difficult. I don't see that it has any advantages.
---
Steve Clamage, stephen.clamage@eng.sun.com

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