From: 7stud -- <bbxx789_05ss@...>
Date: 2011-02-25T05:59:55+09:00
Subject: why is $1 in a grep() equal to nil?

class DataSource
    def get_cpu_info
        "cpu8001"
    end
    def get_cpu_price
        101
    end

    def get_mouse_info
        "mouse241"
    end
    def get_mouse_price
        40
    end
end

DataSource.new.methods.grep(/^get_(.*?)_info$/) do |meth|
    puts "---#{meth}---"
end

--output:--
---get_cpu_info---
---get_mouse_info---


class Computer
    def initialize(an_id, data_source)
        @id = an_id
        @ds = data_source

        @ds.methods.grep(/^get_(.+?)_info$/) do

            puts "-->#{$1}<---"

            Computer.send(:define_method, $1.to_sym) do
                puts "****" + $1 + "****"   #***NIL NIL NIL NIL

                info = @ds.send("get_#{$1}_info".to_sym)
                price = @ds.send("get_#{$1}_price".to_sym)

                alert = ""
                if price > 100
                    alert = "*"
                end

                puts "#{alert} #{info} #{price}"
             end
        end
    end

end



comp1 = Computer.new(1, DataSource.new)
puts comp1.mouse


--output:--
Line 32:in `+': can't convert nil into String (TypeError)
  from t.rb:32:in `mouse'
  from t.rb:52

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