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From: agn@unh.cs.cmu.edu (Andreas Nowatzyk)
Newsgroups: comp.lang.c++
Subject: Re: goodbye cpp ??? (macros vs. inline functions)
Message-ID: <3637@pt.cs.cmu.edu>
Date: 21 Nov 88 22:58:39 GMT
References: <6590072@hplsla.HP.COM> <1757@dataio.Data-IO.COM>
Organization: Carnegie-Mellon University, CS/RI
Lines: 45

Bjarne Strousrup's C++ book claims that inline functions
eliminate the need for most uses of macros and other
cpp-features. I find that statement overly optimistic and
plain false in many actual cases. Using the ATT version 1.2.1
of C++, I found inline functions to be inadequate because:

a) They produce poor code: Everything becomes one large
   comma-expression. Even optimized, the resulting assembly
   code is awful.

b) They lack control of temporary variables and/or objects.
   Numerous temporary variables are being added - frequently
   without need. Since my C-compiler doesn't optimize the use
   of registers, it is not possible to force inline functions
   to keep certain temporary variables in registers.

c) They have a lot of restrictions (inability to use functions
   that don't return values, no loops, troublesome nesting, etc.).

d) They lack control of instantiation: 2 (identical) 
   int inline function appear as the operands to an "==": the
   left inlines normally, the right is replaced by a function call!
   In this case, replacing an inline with an function call is
   fatal to the program (1), but the compiler doesn't even issue
   a warning.

e) No reasonable substitute for conditional compilation: in some
   modules certain functions have to be modified and parts of
   the function would not compile in that environment.

The bottom line is - for now - that inline-function are not even
close to replacing cpp. Note that performance is not the only reason:
lacking control on when and how to expand can result in incorrect code.

   --  Andreas

(1): In case you wondered how this can happen: the inline-function
     needs to know the line-number of where it appears in the source code.
     Is is part of an instrumentation package for parallel code running
     on a simulated multiprocessor.
-- 
   --  Andreas Nowatzyk  (DC5ZV)

   Carnegie-Mellon University	     Arpa-net:   agn@unh.cs.cmu.edu
   Computer Science Department         Usenet:   ...!seismo!unh.cs.cmu.edu!agn
--