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From: schmidt@glacier.ics.uci.edu (Doug Schmidt)
Newsgroups: comp.lang.c++,gnu.g++
Subject: Re: Default argument values
Message-ID: <20077@paris.ics.uci.edu>
Date: 25 Jul 89 18:09:14 GMT
References: <FOX.89Jul23151217@cs.cs.columbia.edu> <43253@bbn.COM>
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Reply-To: schmidt@glacier.ics.uci.edu (Doug Schmidt)
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Organization: University of California, Irvine - Dept of ICS
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In-reply-to: lpringle@bbn.com (Lewis G. Pringle)

In article <43253@bbn.COM>, lpringle@bbn (Lewis G. Pringle) writes:
>In article <FOX.89Jul23151217@cs.cs.columbia.edu> fox@cs.cs.columbia.edu (David Fox) writes:
>>The way to do this is to allow caller to name the parameters
>>the way Ada does:  foo(parm1 = a, parm3 = b, parm2 = c).
>
>I second the emotion, but it may be harder than it looks.  What your are
>describing (I think) are called keyword parameters.  The difficulty,
>is that they impose even more ambiguity into the language.  Default params,
>together with overloading, and conversion operators, already add
>lots ambiguity - keyword paramers would make things even worse.

There's also another problem.  Allowing ``named parameters,'' a la
Ada, weakens information hiding, since formal parameter names are now
visible *outside* their original scope!

For example, consider the effect of changing a formal parameter name
in C or C++.  All you need to modify are the uses of this formal
parameter name *inside* the enclosing function.  This change is
trivial to perform using an interactive query-replace editor feature.

On the other hand, in a language that allows named parameters you need
to hunt down all instances of the formal parameter names occurring in
all *calls* to the function.  These calls are potentially spread
throughout many source files, and it becomes difficult to change the
names in an automated fashion, for the reasons alluded to above.

IMHO, named parameters are another Ada (mis)feature that adds
gratuitous complexity to the compiler and programmer without providing
much value-added benefit.

Doug
--
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