From: Dennis Newbold <dennisn@...>
Date: 2002-03-30T11:18:07+09:00
Subject: Re: Now that's surprising.

Your example, in a more verbose form is equivalent to:

result = true

result = if not result
             false
         else
             nil
         end

or, equivalently,

result = unless result
             false
         else
             nil
         end

The problem is that the "else nil" is not visibly seen, but is implied
by the semantics of the if statement, which, like any other expression,
must return something as the result of its execution.  Its compounded
by the fact that in many languages, if / unless are not viewed as
expressions, but as control statements.Many languages do things
implicitly, such as constructors / destructors in C++, implicit code
conversions in C, etc.  Once you are used to them, you really don't
even think about them much.  I think we can be grateful the Ruby has
very few "surprises" of this nature.  I suggest that in the future,
perhaps you can get in the habit of always explicitly specifying your
own else clause when using the if statement as an expression.  It also
makes things more understandable for yourself and other readers of
your code.  For example,

result = true

result = unless result then false else true end

FWIW.

Dennis

On Fri, 29 Mar 2002, Chris Gehlker wrote:

> Does anyone else think that the following little program is  an instance of
> Ruby violating the POLS by producing nil? I can fix it by uncommenting the
> commented line but I don't think that that should be required.
> 
> def truthTest
>     result = true
>     result = false unless result
>     # return result
> end
> 
> p truthTest
> 
> -- 
> There is, nevertheless, a certain respect and a general duty of humanity
> that ties us, not only to beasts that have life and sense, but even to
> trees and plants. -Michel de Montaigne, essayist (1533-1592)
>