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From: schmidt@zola.ics.uci.edu (Doug Schmidt)
Newsgroups: comp.lang.c++
Subject: Re: Exception handling and transaction management?
Message-ID: <19176@paris.ics.uci.edu>
Date: 6 Jul 89 04:11:27 GMT
References: <546@voodoo.UUCP> <6590181@hplsla.HP.COM>
Sender: news@paris.ics.uci.edu
Reply-To: schmidt@zola.ics.uci.edu (Doug Schmidt)
Organization: University of California, Irvine - Dept of ICS
Lines: 55

In article <6590181@hplsla.HP.COM>, jima@hplsla (Jim Adcock) writes:
>>re: iterations
>>
>>  basically, some linguistic concept that allows you to iterate
>>  over the contents of a class, e..g, a bag, a list, a whatever.
>>
>>  while it's true that C++ doesn't have iterators, it's not clear
>>  that it needs them. Libg++ has the Pix (pseudo-index) class
>>  that resolves this problem (albeit, perhpas not as `nicely'
>>  as the iterators in clu).
>>
>>  this is an important concept, but it's not clear that it needs
>>  linguistic methods to be possible.
>
>The emerging standard for iterators seems to be overloading operator()()
>to provide interation.

There is a group of researchers at the University of Wisconsin that
are implementing an interesting C++ superset called E (I guess that's
really (C += 2) ;-)).  One useful extension they've added is Clu-style
iterators.

Here's a contrived example that demonstrates the usage:

----------------------------------------
iterator char *getstr (char **argv)
{
  while (*argv)
    yield *argv++;
}

main (int argc, char **argv)
{
  iterate (char *s = getstr (argv))
    printf ("item = %s\n", s);
}
----------------------------------------

The C++ syntax is quite clean (although the underlying generated C
implementation is pretty hairy).

In addition to iterators, the main language extensions that E provides
are generic classes (sort of like the templates described in
Stroustrup's paper), persistent data base types, and
honest-to-goodness nested classes (the way they are *supposed* to
work, i.e., like nested records in Ada or Pascal!!).

There is a tech report that describes the E language, also.

Doug Schmidt
--
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