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

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

They may or may not implement the EXISTS() and DEFINED() methods differently. For example, there isn't the concept of undef with hashes that are tied to DBM* files. This means the true/false tables above will give different results when used on such a hash. 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.

Source: Perl FAQ: Data Manipulation
Copyright: Copyright (c) 1997 Tom Christiansen and Nathan Torkington.

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