From: Dossy <dossy@...>
Date: 2002-08-13T00:27:11+09:00
Subject: Re: Ruby Language Q's

On 2002.08.12, Justin Johnson <justinj@mobiusent.com> wrote:
> >     yes = "yes"
> >     no = "no"
> >     x = nil
> >     p x.nil? yes: no
> >
> > Hmm.  Not interesting?
> 
> Well, the main thing here is that the '?' and ':' are part of the
> accompanying symbols so they would be classed as part of the symbol name.
> Ruby already does this for symbols ending in '?'.  I don't see what the
> problem is.  If we were talking about a C/C++ parser then that's a different
> matter...

Really?  That surprises me about Ruby ... lets see:

    irb(main):014:0> "".size ? true : false
    true

    irb(main):013:0> "".size? true : false        
    SyntaxError: compile error
    (irb):13: parse error
    "".size? true : false
                   ^
            from (irb):13

Okay, I guess you're right.  If a method is defined having a
trailing '?' then whitespace matters.  Totally surprised me.

But then, this is funny:

    irb(main):003:0> 1 ? true : false
    true

    irb(main):002:0> 1?true:false
    true

There IS no method #1? defined.  Why doesn't the second code
snippet also generate a parse error?  Interestingly:

    irb(main):015:0> true? true : false
    SyntaxError: compile error
    (irb):15: parse error
    true? true : false
                ^
            from (irb):15

    irb(main):016:0> true?true:false   
    SyntaxError: compile error
    (irb):16: parse error
    true?true:false
              ^
            from (irb):16

    irb(main):017:0> true ? true : false
    true

I would not have expected the middle code snippet to generate
a parse error (given that "1?true:false" doesn't) ... since
#true? isn't a defined method, either.

This is all using:

$ ruby -v
ruby 1.6.7 (2002-03-19) [i386-linux]

It also happens in Ruby 1.7.2 as well:

$ ruby-1.7.2 -v
ruby 1.7.2 (2002-05-30) [i686-linux]

> Also, 'yes:' would only be valid inside a method argument list and so would
> cause a parsing error in this case.

Why would it cause a parsing error?  Really, it would cause an
"ArgumentError: wrong # of arguments(1 for 0)" as #nil?'s arity
is 0, but (if the named parameter "foo: bar" was implemented)
you would be passing it 1 arg, the object referenced in variable
"no" as the "yes" parameter to #nil? which doesn't exist.

-- Dossy

-- 
Dossy Shiobara                       mail: dossy@panoptic.com 
Panoptic Computer Network             web: http://www.panoptic.com/ 
  "He realized the fastest way to change is to laugh at your own
    folly -- then you can let go and quickly move on." (p. 70)