ruby - 2

class MagGreeter
    attr_accessor :name;
    def initializer(name = "World")
        @name = name;
    end
    
    def sayhi
        if @name.nil? #只有当@name = nil的时候，@name.nil?才为真。
            puts "...";
        elsif @name.respond_to?("each")
            @name.each do |name|
                puts "hi #{name}";
            end
        else
            puts "hi #{@name}";
        end
    end

    def saygoodbye
        if @name.nil
            puts "..."
        elsif @name.respond_to?("join")
            puts "goodbye, " + @name.join(",");
        else
            puts "goodbye #{@name}";
        end
    end
end
if __FILE__ == $0
    a = MagGreeter.new;
    a.name = "liujun";
    a.sayhi;
    a.name = ["pretty gril", 'mike'];
    a.sayhi;
    a.name = nil;
    a.sayhi;
    puts nil.nil?;
    puts ''.nil?; #=>false,ruby里面，空字符并不是nil对象。
end