Re: SELinux userspace infrastructure language

[Stephen Bennett <spb@gentoo.org>]

On Wed, 6 Jun 2007 11:28:04 -0400
"Joshua Brindle" <jbrindle@tresys.com> wrote:

> >>> Not certain what you mean - you mean the private variables? You
> >>> can use the PIMPL idiom - http://www.codepedia.com/1/CppPimpl -
> >>> but I'm not convinced it's worth the pain. After the care we took
> >>> to hide implementation in libsepol we didn't really make changes
> >>> that would have broken in the ABI. 
> >>> 
> >> 
> 
> How painful is it? The examples on that page don't look too bad, and
> they claim it reduces compile time (something you've already griped
> about)

It's not painful really, even for very small or very large classes. If
you're using it a lot in a given library it's not too hard to add a few
templated utility classes to make life somewhat easier either.

> So are we going to have to pad it to be able to add stuff later on?
> Would adding something in the public part shift the private part down
> in a way that would break the ABI? This worries me a bit, I know QT
> does padding to handle this but I haven't looked at what they do
> specifically.

The public part should consist solely of one or two pointers --one to
the private implementation part, and possibly one to the vtable if it
has virtual functions. That sort of ABI is extremely resilient, and
members (both data and functions) can be added without breaking it.

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