From: Benoit Daloze <eregontp@...>
Date: 2009-12-18T19:09:11+09:00
Subject: Re: Suggestion of Array#=== which improves case/when behavio

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Hi,

It doesn't look too usefull to me like that. (I mean using classes to
compare).

For this purpose I wrote something like:

# Analyse arguments given to a method(*args)
#
# Exemple:
# def m(*args)
#   case args
#     when ARGS[Complex]
#       m(Complex.new(1,1))
#     when ARGS[Integer, Boolean]
#       m(2, true)
#     when ARGS[[Numeric, Float], String]
#       m([1, 3.14], "Hello World!")
#     when ARGS[[[Integer, Integer],[Float, Rational     ]]]
#       m(      [[1      , 2      ],[3.0  , Rational(1,2)]])
#   end
# end

module Boolean; end
class FalseClass; include Boolean; end
class TrueClass;  include Boolean; end

class ARGS
    def initialize(*constraints)
        @constraints = constraints
    end

    def ARGS.[](*constraints)
        ARGS.new(*constraints)
    end

    def match?(args)
        return false unless @constraints.length == args.length
        @constraints.each_with_index { |constraint, i|
            case constraint
            when Module
                unless args[i].is_a?(constraint)
                    return false
                end
            when Array
                unless args[i].is_a?(Array) &&
ARGS[*constraint].match?(args[i])
                    return false
                end
            end
        }
        true
    end

    def ===(args)
        match?(args)
    end
end

-------

Some mails ago, I also thought Array#=== implemented a OR-related test like
in:
case 2
when -1,1,2
  ...
end

But that seems to be more a feature of the "block" case.

So, I think this trick can be useful in special "cases", but I don't see
enough interest to do that for the Ruby core.

Any exemples more attractive ?

2009/12/18 Dmitry Vazhov <dmitryelastic@gmail.com>

> So, my question is: Do you agree that Array#=== can be useful for us?
>
> My opinion is that it can be in ruby std library along with
> Proc#===(which is already in ruby 1.9 --
>
> http://www.aimred.com/news/developers/2008/08/14/unlocking_the_power_of_case_equality_proc/
> )
>
> --
> Posted via http://www.ruby-forum.com/.
>
>

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