Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!cs.utexas.edu!uunet!ficc!cliff
From: cliff@ficc.uu.net (cliff click)
Newsgroups: comp.lang.misc
Subject: Re: Language Tenets
Summary: q/r, returning structs
Message-ID: <5096@ficc.uu.net>
Date: 19 Jul 89 20:50:11 GMT
References: <57125@linus.UUCP> <1989Jun24.230056.27774@utzoo.uucp> <1989Jul17.184707.415@maths.nott.ac.uk>
Organization: Ferranti International Controls
Lines: 43

In article <1989Jul17.184707.415@maths.nott.ac.uk>, anw@maths.nott.ac.uk (Dr A. N. Walker) writes:
> [Good contributions from, inter alia, cik@l.cc.purdue.edu (Herman Rubin),
> pds@quintus.UUCP (Peter Schachte), roelof@idca.tds.PHILIPS.nl (R. Vuurboom),
> and suitti@haddock.ima.isc.com (Stephen Uitti) on the problem of "q r <- t/b".]
> 
>    (a)  Is it a language deficiency if "q r <- t/b" cannot be sensibly
> written?  Answer:  yes.  Solutions on the lines of
> 
> 		q = t/b; r = t%b; /* "and the optimiser should tidy up" */
> 
> are inadequate because I might want to write
  [deleted expressions with side effects...]

Perhaps what we want is the ability to return a structure for any
function call (even an infix or inlined one), and the ability to assign
that structure to a mongrel structure we create on the fly.

Given:  struct{ float q, r; } divrem( float t, b );
and:    float q[10], r[10], a[10], b[10];

we get: struct{ q[3], r[9] } = divrem( a[2], b[3] );
or:     struct{ q[i++], r[j++] } = divrem( a[i], b[j] );

The lvalue is a structure of lvalues, each of the correct type for the
structure but perhaps changing with each usage.  This ability could be
used to *pass* a structure we create on the fly, instead of filling in
the fields in a temp structure:

     struct timething { int h, m, s };
     void printime( struct timething foobar );
     int hour, min, sec;

     [expressions using/setting hour, min, sec...]

     printime( struct timething { hour, min, sec } );


Flames, anybody?

-- 
Cliff Click, Software Contractor at Large
Business: uunet.uu.net!ficc!cliff, cliff@ficc.uu.net, +1 713 274 5368 (w).
Disclaimer: lost in the vortices of nilspace...       +1 713 568 3460 (h).