FAQ 4.63 Why don't my tied hashes make the defined/exists distinction?

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4.63: Why don't my tied hashes make the defined/exists distinction?

    This depends on the tied hash's implementation of EXISTS(). For example,
    there isn't the concept of undef with hashes that are tied to DBM*
    files. It also means that exists() and defined() do the same thing with
    a DBM* file, and what they end up doing is not what they do with
    ordinary hashes.


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