Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!cmcl2!kramden.acf.nyu.edu!brnstnd
From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.lang.misc
Subject: Re: := versus ==
Message-ID: <17559:Aug101:50:5290@kramden.acf.nyu.edu>
Date: 1 Aug 90 01:50:52 GMT
References: <1990Jul30.143530.24295@phri.nyu.edu> <25684@cs.yale.edu> <=L-4T-A@ggpc2.ferranti.com>
Organization: IR
Lines: 22
X-Original-Subject: Re: He's not the only one at it again!

In article <=L-4T-A@ggpc2.ferranti.com> peter@ficc.ferranti.com (Peter da Silva) writes:
> I think the best solution to this is to use ":=" for assignment and "==" for
> equality. That way there would be no problem with using the wrong one in the
> wrong context by accident.

Q has a better solution.

  a == b is for comparison. Its value is 1 if they're equal, 0 if not.
  a := b is for assignment. It sets a to b and has value a.
  a = b is for assignment. It sets a to b and has no value.

Advantages over straight ==/:= and over C:

if(a = b) is invalid, and if(a := b) is easy to notice.

You can still use = for normal assignment, so you don't get confused by
the new notation.

The compiler can check that *every* value is used, rather than just
ignoring assignments. a = b := c := d feels and looks right.

---Dan