Newsgroups: comp.lang.c++
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Can we hide the private part of a class ?
Message-ID: <1988Oct5.172203.8385@utzoo.uucp>
Organization: U of Toronto Zoology
References: <1358@stratus> <1988Sep29.044111.16104@utzoo.uucp> <4193@polya.Stanford.EDU> <1988Oct2.045604.17456@utzoo.uucp> <5922@june.cs.washington.edu>
Date: Wed, 5 Oct 88 17:22:03 GMT

In article <5922@june.cs.washington.edu> david@uw-june.UUCP (David Callahan) writes:
>Changing the size or position of private elements changes only the 
>offsets of the public elements. These could be treated as external 
>variables and bound at link time rather than compile time. There might
>small performance penalty...

There will be a large performance penalty on many modern machines, unless
the linker is smart enough to practically redo the code generation to
compensate.  Things like limited-range offset addressing modes, which are
very common, really do require knowing the offset at code-generation time
to avoid having to generate much slower worst-case code.

>Inline functions are real compilation dependences and can not be hidden by late
>binding, but the orginal poster's intent was to hide implementation details, 
>not avoid recompilation when public information changes, 

Inline functions are an optimization; their contents are no more "public
information" than the types and sizes of private members.
-- 
The meek can have the Earth;    |    Henry Spencer at U of Toronto Zoology
the rest of us have other plans.|uunet!attcan!utzoo!henry henry@zoo.toronto.edu