From: Gregory Seidman <gsslist+ruby@...>
Date: 2006-03-29T21:42:29+09:00
Subject: Re: Why do some methods names which replace the content in place doesn't have the "!" sign?

On Wed, Mar 29, 2006 at 05:50:30PM +0900, Peter Hickman wrote:
[...]
} Fine, now say how this is supposed to be of benefit to Ruby. What does 
} it make doing in Ruby easier and safer than the present way we go about 
} doing it?
[...]
} This is my point, there was no "sufficiently compelling and clear 
} argument" given other than it is available in C++.

I don't know that it is of great benefit to Ruby, honestly. I certainly
found it valuable in C++, but that had a lot to do with a need to provide
libraries with as much in the way of machine-readable documentation (e.g. I
promise I won't delete this object you are passing me) as possible given
that I knew the consumers of the library wouldn't read anything I wrote
about it.

There are certainly advantages to design-by-contract, of which const is a
special case. I'd like to see some machine-readable guarantees of
preconditions and postconditions and invariants and the like in Ruby. Such
guarantees are both debugging aids and optimization hints. For a language
like Ruby, where many of its uses are quick scripts, an actual requirement
to put such guarantees in one's code would be a problem. Optional hints and
assertions are easy, however.

In any language, including Ruby, it is possible to assert preconditions and
postconditions. Invariants are somewhat more difficult without runtime
support. What makes a language truly support design-by-contract is that
these assertions mean something specific to the runtime beyond code to be
executed. No, I can't come up with a Ruby implementation off the cuff.

It is an interesting idea that someone could run with, however, and it is
for that reason that I objected to your stifling dismissiveness. If you
look back at my posts, you will notice that I never defended const, or
enforcing any particular meaning for the ! method suffix. I regarded the
original poster's ideas as interesting, and worth discussing.

--Greg