From ...
From: Erik Naggum <erik@naggum.no>
Subject: Re: What is wrong with OO ?
Date: 1997/02/13
Message-ID: <3064828794077287@naggum.no>#1/1
X-Deja-AN: 218500965
References: <5dr62h$i6o@Masala.CC.UH.EDU>
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Organization: Naggum Software; +47 2295 0313; http://www.naggum.no
Newsgroups: comp.lang.c++,comp.lang.lisp


* cosc19z5@Bayou.UH.EDU
| In C however, you need pointers for tasks which do not require them --
| modifying arguments to functions!

the very existence of a "better" mechanism to do this in C++ (references)
suggest that multiple return values really do make a lot of sense, despite
all the hostile arguments from certain camps when you suggest this.  that a
widely used tool like `perl' also supports them as a matter of course, and
to its users delight, is perhaps indicative of a fundamental flaw in the
argument that functions in programming languages should only return one
value, as opposed to functions in mathematics, which already differ greatly
from "our" functions.

incidentally, I happen to dislike the approaches to faking the return of
multiple values that don't actually return multiple values: structs in C,
lists in Scheme, OUT arguments in Ada, NAME in Simula, VAR in Pascal,
references (mere syntactic sugar for pointers) in C++, etc.

my favorite example is getting the current time under Unix and in C:
`gettimeofday' takes two pointers to structures you have to declare and
possibly allocate memory for, fills them in for you, and then you get to
retriev the values from them.  the function returns four integers in this
very complicated way: seconds since the epoch, microseconds into the
current second, time zone as the number of minutes west of Greenwich, and
the type of daylight savings time to apply.  let's also not forget that
`gettimeofday' includes an error return value to indicate only one kind of
error: "an argument address referenced invalid memory", or a stray pointer.
to decode this time into your current timezone, you need to decode it with
the function `localtime', which, unsurprisingly, takes a pointer to the
first return value from `gettimeofday' and returns a pointer to statically
allocated memory that contains the values you need in a structure.  you
need to make certain that you copy all of these values to your own space
before some other function clobbers it.  `localtime' returns 11 values,
most of which you don't need.  (and then, of course, the day of the month
is a number in the range 1-31, but the month is a number in the range 0-11
and the year is 1900 less than the actual year, but that's another can of
worms.)  all this to achieve the effect of multiple return values!  to
summarize: `gettimeofday' requires pointers to preallocated memory to
return multiple values, and has an error return value to barf on the
address of that memory, while `localtime' returns a pointer to a static
memory area overwritten by each call.  this epitomizes the Unix interface
as I see it -- Unix doesn't give its programmers the time of day.

#\Erik
-- 
my other car is a cdr