|Perl Language Reference Manual|
by Larry Wall and others
Paperback (6"x9"), 724 pages
RRP £29.95 ($39.95)
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The bucket usage information provided by
scalar(%hash) is not
available. What this means is that using %tied_hash in boolean
context doesn't work right (currently this always tests false,
regardless of whether the hash is empty or hash elements).
Localizing tied arrays or hashes does not work. After exiting the scope the arrays or the hashes are not restored.
Counting the number of entries in a hash via
scalar(values(%hash)) is inefficient since it needs to iterate
through all the entries with FIRSTKEY/NEXTKEY.
Tied hash/array slices cause multiple FETCH/STORE pairs, there are no tie methods for slice operations.
You cannot easily tie a multilevel data structure (such as a hash of hashes) to a dbm file. The first problem is that all but GDBM and Berkeley DB have size limitations, but beyond that, you also have problems with how references are to be represented on disk. One module that does attempt to address this need is DBM::Deep. Check your nearest CPAN site as described in "Writing new modules and finding existing ones" (perlmodlib) in the Perl Library Reference Manual (Volume 2) for source code. Note that despite its name, DBM::Deep does not use dbm. Another earlier attempt at solving the problem is MLDBM, which is also available on the CPAN, but which has some fairly serious limitations.
Tied filehandles are still incomplete. sysopen(), truncate(), flock(), fcntl(), stat() and -X can't currently be trapped.
|ISBN 9781906966027||Perl Language Reference Manual||See the print edition|