Path: utzoo!attcan!uunet!ogicse!decwrl!elroy.jpl.nasa.gov!usc!wuarchive!mit-eddie!apollo!williams_j
From: williams_j@apollo.HP.COM (Jim Williams)
Newsgroups: comp.lang.c++
Subject: Re: Request for C++ coding "guidelines"
Keywords: C++, inlines
Message-ID: <48ccd464.20b6d@apollo.HP.COM>
Date: 22 Feb 90 18:25:00 GMT
References: <4446@pegasus.ATT.COM> <4843@helios.ee.lbl.gov> <84@pascal.decvax.UUCP>
Sender: root@apollo.HP.COM
Lines: 17

This brings up an important reason for using inlines.  The example
class I have is too long to be included here, but it contains a number of member
functions, all declared "inline", which perform numerical calculations.  By
expanding these inline, the C compiler optimizer is able to eliminate the 
majority of these calculations because the results are never used.  A lot
of the rest of the calculations can be done at ("C") compile time because the
complier knows the value of the arguments passed to the functions.
     The performance increase therefore far exceeds the overhead of the function
call and may be closer to an order of magnitude.
     If these functions were not "inlined", some of the performance could be 
gotten back by adding some record keeping to the class so that it could be
determined at run time which values actually needed to be calculated.  This
would add complexity, however. Also, I don't see any way to force computations
to be done at compile time for non-inlined functions.

     My vote is that if a function is declared "inline", it should either be
implemented inline, or if not possible, flagged as an error.