Are you familiar with globs? Skip the next paragraph if you
are and I will answer the question.
You are familiar with the concept that we can have $I, @I, %I,
sub I {}, and a file handle called I? A glob ( indicated by
the *I ) is a convenient way of referring to all of them at
once.
Basically, the *I{HASH} construct means we are only referring
to the HASH part if the glob. When the assignment is done
( *I = getSlashConf() ), we are certain that
only the HASH portion of the glob will be reassigned. After
the assignment, %I now refers to whatever getSlashConf returns
and we can treat it like a normal hash, or in this case, a hash
of hashes. It is a clever way of returning a reference without returning
a reference.
If you are not familiar with globs, get yourself a copy of Conway's Object Oriented Perl,
because he explains what globs are, how they work and what this
kind of assignment is doing in a very clear and concise way.
Mik
Mik Firestone ( perlus bigotus maximus ) | [reply] |
It's a Perl 4 relic in a shiny new Perl 5.6 world. (As Perl 5 came out in 1994, well, there's not much excuse to do things this way.)
What would be better is returning a reference to a hash from getSlashConf(). That code might look something like this:
my $l = getSlashConf();
getSlash();
my $op = $l->{F}{op};
In getSlashConf(), that last line should probably change to:
return $l{HASH};
In my opinion, this makes it more clear that we are dealing with a hash of hashes data structure. (All that means is that the value of a hash is actually a reference to another hash, instead of a scalar.)
For more information on references, see perlman:perlref. For more information on complex data structures, see perlman:perldsc. | [reply]
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W/r/t the question about what's $I{F}{op}--are you familiar
with multidimensional data structures? This looks to be a
hash of hashes, in this case. Perl implements
multidimensional data structures using references--so you
have a regular hash, %I, with a key called "F"; and the
value of that key is a reference to another hash (a
reference is a scalar, and a hash value can only be a
scalar, so that works out).
So you could say:
my $hash_ref = $I{F};
Now you've got a hash ref in $hash_ref, and you can
dereference it to see what it holds. You could now say:
my $op = $hash_ref->{'op'};
So, if we put those together and eliminate the temporary
variable, we get
my $op = $I{F}->{op};
which is the same as
my $op = $I{F}{op};
because Perl lets you eliminate the dereferencing arrows
between brackets subscripts.
Take a look at perlref, perldsc, and perllol. | [reply]
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