Hello Monks,

The several answers are spot-on, including encouraging the writer to use the debugger, but I have a curious issue that is somewhat related, to wit: for my amusement I've written three great circle calculators (Spherical Law of Cosines, Haversine and Vincenty Inverse; C, Perl and Python versions) that stores airport locations and their geodesic parameters (latitude and longitude) in a Btree BerkeleyDB. The hash instances are tied with MLDBM. I load them into the DB from a tab-delimited file. Here is my airport hash definition:

$APref->{++$id} = { APname => $loc,
  geodesics => [ $lat, $long, dms2rad($lat), dms2rad($long) ]
};

[download]

$APref is a hash reference. The key is an interger rather than a location string so I can say, for example; calculate the GC distance between 17 and 33. When I access that array, as in when printing out a list or passing two airport instances to my GC calculators I would like to say:

$APref->{$key}{geodesics}->[0..3]

but this causes Perl (5.38.2) to barf. This expression

@{$APref->{$key}{geodesics}}[0..3]

is the only way to fetch that slice. My standard rule is to use the arrow operator wherever there is a reference in such an expression, but the block indirection version is the only syntax that works, in this case. Is their something about taking an array slice that defeats the arrow operator, or am I missing something? I have no problem using or understanding that noisier indirection syntax, but there must be an explanation beyond my current understanding of the arrow operator. Thoughts please?

U P D A T E

Thank you LanX and tybalt89. You're never too old to learn something you didn't know about Perl.

->@[0..3]

is exactly what I was looking for, and context is everything; a slice is not a scalar.

In reply to Re^2: Hash syntax by perlboy_emeritus
in thread Hash syntax by mvanle

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