From: dblack@...
Date: 2007-02-23T13:22:53+09:00
Subject: Re: Ruby's "case" doesn't behave like a normal switch

Hi --

On Fri, 23 Feb 2007, Guillaume Nargeot wrote:

> The problem with ruby is that you can't use a switch as it behaves with many
> other languages like C, php, etc.

I don't consider that a problem.  If all languages had to behave
exactly the same way, there would only be one language, and we'd all
get bored :-)

> This is not perfect, because you have to change your syntax, but it might be
> quite useful in some cases.
>
> # Redefine the === method of the Array class, that is used to match the
> argument
> # of the "case" directive.
> class Array
>  # Return true if self contains any element of the given parameter.
>  def ===(o)
>    o.each do |e|
>      return true if self.include?(e)
>    end
>    false
>  end
> end
>
> # Example 1
> x = ["case4"]
>
> case x
>  when ["case1", "case2"]
>    puts "first case"
>  when ["case3", "case4", "case5"]
>    puts "second case"
>  when ["case6"]
>    puts "third case"
>  else
>    puts "not matched"
> end
>
> # Returns: "second case"
>
> # Example 2
> x = [6]
>
> case x
>  when [1, 2]
>    puts "first case"
>  when [3, 4, 5]
>    puts "second case"
>  when [6]
>    puts "third case"
>  else
>    puts "not matched"
> end
>
> # Returns: "third case"
>
> What do you think about it ?

It's very dangerous.  Remember that changing Array#=== changes it
everywhere.  There may be places in Ruby itself, or in other libraries
you're using, that depend on the original behavior.


David

-- 
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