From: Robert Klemme <shortcutter@...>
Date: 2010-09-03T16:07:39+09:00
Subject: Re: case (variable) when type1 ... when type2 ... end

On Fri, Sep 3, 2010 at 7:25 AM, tilde <tilde@autistici.org> wrote:
> On 08/30/10 10:33, Jean-Julien Fleck wrote:
>>>
>>> how can I write case statement to check of specific type the variable
>>> has?
>>> Something like:
>>
>> It simpler:
>>
>>> case var
>>> when :Fixnum
>>>  puts "#{var} is Fixnum"
>>> when :String
>>>  puts "#{var} is String"
>>> end
>>
>> case var
>> when Fixnum
>>  puts "#{var} is Fixnum"
>> when String
>>  puts "#{var} is String"
>> end
>>
>> (no ":")
>>
>> Cheers,
>>
>
> Hi, could you explain me why this works? It's a special behaviour of the
> "case" statment?

"case" uses operator "===" to check conditions.  If you do "case x
when y" then "y === x" is invoked to check the condition (note the
order of x and y).  You can even cook your own

positive = lambda {|x| x >= 0}
class << positive
  alias :=== :call
end

(-4..4).each do |i|
  case i
  when positive
    puts "#{i} pos"
  else
    puts "#{i} neg"
  end
end

btw, there is also another form of case

case # no value here!
when i >= 0
  puts "#{i} pos"
else
  puts "#{i} neg"
end

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/