理解困難

>> a1=Array.new(2)
=> [nil, nil]
>> a1.map{|e|e.object_id}
=> [4, 4]
>> a1[0]=:test
=> :test
>> a1
=> [:test, nil]

>> a2=Array.new(2,Array.new(2))
=> [[nil, nil], [nil, nil]]
>> a2.map{|e|e.map{e.object_id}}
=> [[2983450, 2983450], [2983450, 2983450]]
>> a2[0][0]=:test
=> :test
>> a2.map{|e|e.map{e.object_id}}
=> [[2983450, 2983450], [2983450, 2983450]]
>> a2
=> [[:test, nil], [:test, nil]]