From: Robert Dober <robert.dober@...>
Date: 2008-04-20T03:32:26+09:00
Subject: Re: How to "break" a "case-when" ?

On Sat, Apr 19, 2008 at 7:59 PM, Christopher Dicely <cmdicely@gmail.com> wrote:
> On Fri, Apr 18, 2008 at 1:40 PM, Robert Dober <robert.dober@gmail.com> wrote:
>  >
>  > 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.
>
>  Sure it will. There are two different forms of case, the form
First my appologies for my error, I did not see that the case part was
empty, my fault
>  case
>   when foo1 then bar1
>   when foo2 then bar2
>   ...
>   else baz
>  end
>
>  Works exactly as described above.
>
>  You could do it with the other kind of case (the one whose semantics
>  you describe),
>  but it would be a bit uglier. E.g.,
>
>  case num
>   when (if var.between? 0, 10 then 1 else Object.new) then do_normal_stuff
>   when 1 then do_error_stuff
>   ...
>  end
>
>
my point is however that of course you lose the basic feature you
wanted but we have two possibilities here, either monkeypatching
TrueClass and using the !! form to convert any logical true value to
the real single true value, than the code might look like this

case expression
    when /abc/
        ...
     when !! get_an_object(expression)
        ...

I have to admit that the monkey patch is just not an option if you are
writing a library and is a feature too often abused anyway.

I therefore suggest to follow Christopher's approach even if the code
gets a little bit uglier (but beauty lies in the eyes of the
beholder).

case
    when /abc/ === expression
       ...
    when get_an_object( expression )
       ...
end

Sorry again, I outsmarted myself ;)

Cheers
Robert


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