1. pseudo-hashes are deprecated
the "pseudo-hashes are deprecated" error means you're trying to access an array as a hash, which means that either$data->or$data->is an arrayref.
2. defined 解釋
用於判斷變數是否為 undef，未定義， 不能用於陣列和hash
many folks tend to overusedefinedand are then surprised todiscover that the number0and""(the zero-length string) are, in fact,defined values.
0and""(the zero-length string 用 if () 來判斷即可
3. or || 和 and &&的區別
本身沒有區別，習慣問題 ，但是有時候牽涉到運算子優先順序的問題，結果會不同
left &
left | ^
left &&
left || //
nonassoc .. ...
right ?:
right = += -= *= etc.
left , =>
nonassoc list operators (rightward)
right not
left and
left or xor
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