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

Discussion in 'Perl Misc' started by PerlFAQ Server, Mar 27, 2011.

  1. This is an excerpt from the latest version perlfaq4.pod, which
    comes with the standard Perl distribution. These postings aim to
    reduce the number of repeated questions as well as allow the community
    to review and update the answers. The latest version of the complete
    perlfaq is at http://faq.perl.org .

    --------------------------------------------------------------------

    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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    are not necessarily experts in every domain where Perl might show up,
    so please include as much information as possible and relevant in any
    corrections. The perlfaq-workers also don't have access to every
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    PerlFAQ Server, Mar 27, 2011
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