From: "Hal E. Fulton" <hal9000@...>
Date: 2003-06-18T08:01:53+09:00
Subject: Re: [RCR] Array#push(empty array expanded) => no exception

----- Original Message -----
From: "ahoward" <ahoward@fsl.noaa.gov>
Newsgroups: comp.lang.ruby
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Tuesday, June 17, 2003 4:07 PM
Subject: Re: [RCR] Array#push(empty array expanded) => no exception


> > For one thing, what if a variable is passed in?  We don't want it to
fail
> > just because the array is empty.
>
> well this is not *exactly* the case simon described though is it?
>
>   method []   # empty array as arg
>   method *[]   # NO args!

Well, I meant more like this case:

  myvar = mymethod  #  mymethod returns an array... possibly empty
  meth2(*myvar)     # Pass that array as individual args

> so, it's not that the method is failing just because an empty array is
passed
> in, it is failing because an empty array was exploded, yielding and
> non-existent parameter list.  i may be in the minority, but it's not THAT
> counter intuitive for me that attempting to call a method expecting args,
with
> no args, should be an error.

The asterisk (or star or splat) is a special case.
I can't think of a case where Ruby generates a
"number of params" type of error for a method where
star is specified where the method is defined.

On the other hand, I am simply *assuming* that there
is a star on the definition. There certainly is one
on the call... they usually go together, UNLESS you
are expanding an array of known size, resulting in
exactly N parameters.

> > For another thing, consider what happens with
> > strings. foo = "value" + "" should not be
> > illegal, I think.
>
> no, of course not.  but this is analogous to the first example above, not
the
> second one, which would be more along the lines of
>
>   foo = "value" + *""
>
> if '*String' did, for example, an explosion into a list of Fixnums (chars)
or
> something like that...

Well, I see what you mean. But they are analogous in
this sense: Given a collection of entities, add another
entity that is a "null" with respect to the context of
that collection and its add operation.

Pushing an empty list of items onto an array doesn't
change the array, just as adding a null string onto
a string doesn't change that string; except that we
are actually doing an assignment where the string
is concerned -- better to make it a <<. Boy, this is
getting more and more nitpicky, isn't it?

The bottom line, to me, is that if there is a star
in the definition AND in the caller, the idea of
"expanding" the array is almost meaningless.

Is there ever a real difference in these two situations?
(See below.) There probably is something I'm overlooking,
of course.

   def meth1(*args)
     #...
   end

   meth1(*myarray)

   def meth2(args)
     #...
   end

   meth2(myarray)

Cheers,
Hal