>>>>> "SF" == Steve Fink <[EMAIL PROTECTED]> writes:
SF> I don't think this has been mentioned, although it's really just a
SF> combination of two existing ones: I often have a table of sets.
SF> for my $user (@filenames) {
SF> open(my $fh, "<", $user) {
SF> while(<$fh>) {
SF> $use{$user}{$1} = 1 while /include\s*['"](.*?)['"]/g;
SF> }
SF> }
SF> It's a full graph, with fast looking and iteration over outgoing edges.
i consider graphs a variant of deep (and cyclical) data structures. and
i think they are more complex than the other simple hash uses. also
graphs are too hard to explain in one slide for this class. but i will
keep it in mind as another use. all the classic linked list structures
can be easily done with hashes for sure.
SF> There's sort of another use buried in there, too: hashes can be
SF> used to map object identifiers to their data (a la inside-out
SF> objects or something simpler that is just trying to keep the real
SF> data in a canonical place, perhaps to avoid worrying about cyclic
SF> references.)
i use a hash to track all objects created by a class. the fun part is
that the key and value were the same thing. but the key gets stringified
which is why you still need the ref/object as the value.
SF> Hashes can be used for caches or memoization:
SF> our $answer;
SF> sub func {
SF> return $answer ||= ...compute...;
SF> }
caching is a good one. that is all that memoize uses.
SF> Hashes can be used for sparse arrays:
SF> $arr{10} = "X";
SF> $arr{83719} = "Y";
i mentioned that one.
SF> Hashes can be used for symbol tables. :-)
true. i didn't mention that. but i always teach to use hashes for data
and not the symbol table (via symrefs). mung the symbol table only when
you need to mung it!
thanx,
uri
--
Uri Guttman ------ [EMAIL PROTECTED] -------- http://www.stemsystems.com
--Perl Consulting, Stem Development, Systems Architecture, Design and Coding-
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