From: Robert Dober <robert.dober@...>
Date: 2008-04-19T05:40:57+09:00
Subject: Re: How to "break" a "case-when" ?

On Fri, Apr 18, 2008 at 8:52 PM, Iñaki Baz Castillo <ibc@aliax.net> wrote:
> El Viernes, 18 de Abril de 2008, Peña, Botp escribió:
>
>
>  > how about another case way,
>  >
>  > var = ...something...
>  > case
>  >   when num==1 and ( var < 0 || var > 10 )
>  >      puts "var not valid for num==1 !!!!!"
>  >   when other_stuff_condition
>  >   when ....
>  >      ...
>  >   else
>  >     else_stuff
>  > end
>  > puts "Write it"
>
>  opss, I didn't know that a "when" can contain a comparision, nice to know!
It can contain any expression, but it will not do what you want.
The semantics of case is the following

  case e
     when e1
        a1
     when e2
       a2
    else
       a3
   end

if e1 === e then
    a1
elsif e2 === e then
   a2
else
  a3
end

unfortunately
  case e
     when true
        a

will only work for e == true as
true === Object.new --> false

maybe Matz did not want to allow logical comparision in case ;)

but he gave us the power to overrule

try the following code with the line commented and then uncommented and
you will see what is going on

class TrueClass
#   def === any; true end
end

case 42
   when true
      p true
   else
      p :else
 end
HTH
R.
-- 
http://ruby-smalltalk.blogspot.com/

---
Whereof one cannot speak, thereof one must be silent.
Ludwig Wittgenstein