From: Robert Klemme <shortcutter@...>
Date: 2010-09-04T00:40:12+09:00
Subject: Re: case (variable) when type1 ... when type2 ... end

On 09/03/2010 10:46 AM, tilde wrote:
> On 09/03/10 09:49, tilde wrote:
>> On 09/03/10 09:07, Robert Klemme wrote:
>>> 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
>>>
>> Clear yet concise explaination, thank you!
>
> Also (at least in 1.9.2) the alias is unnecessary, if a proc is provided
> within a "when" statment, the var is automatically passed as proc's
> argument ;)

Oh, that's great!  IIRC I suggested this a while ago.

Thanks for the update!  I haven't played with 1.9.2 yet.

Kind regards

	robert