=head1 DESCRIPTION
Prior to release 5.0 of Perl, a programmer could use dbmopen()
-to magically connect an on-disk database in the standard Unix dbm(3x)
-format to a %HASH in their program. However, their Perl was either
+to connect an on-disk database in the standard Unix dbm(3x)
+format magically to a %HASH in their program. However, their Perl was either
built with one particular dbm library or another, but not both, and
you couldn't extend this mechanism to other packages or types of variables.
enchanted. C<CLASSNAME> is the name of a class implementing objects of
the correct type. Any additional arguments in the C<LIST> are passed to
the appropriate constructor method for that class--meaning TIESCALAR(),
-TIEARRAY(), TIEHASH() or TIEHANDLE(). (Typically these are arguments
+TIEARRAY(), TIEHASH(), or TIEHANDLE(). (Typically these are arguments
such as might be passed to the dbminit() function of C.) The object
returned by the "new" method is also returned by the tie() function,
which would be useful if you wanted to access other methods in
C<CLASSNAME>. (You don't actually have to return a reference to a right
-"type" (e.g. HASH or C<CLASSNAME>) so long as it's a properly blessed
+"type" (e.g., HASH or C<CLASSNAME>) so long as it's a properly blessed
object.) You can also retrieve a reference to the underlying object
using the tied() function.
This method will be triggered every time the tied variable is accessed
(read). It takes no arguments beyond its self reference, which is the
-object representing the scalar we're dealing with. Since in this case
-we're just using a SCALAR ref for the tied scalar object, a simple $$self
+object representing the scalar we're dealing with. Because in this case
+we're using just a SCALAR ref for the tied scalar object, a simple $$self
allows the method to get at the real value stored there. In our example
below, that real value is the process ID to which we've tied our variable.
=item DESTROY this
This method will be triggered when the tied variable needs to be destructed.
-As with other object classes, such a method is seldom necessary, since Perl
+As with other object classes, such a method is seldom necessary, because Perl
deallocates its moribund object's memory for you automatically--this isn't
C++, you know. We'll use a DESTROY method here for debugging purposes only.
=back
That's about all there is to it. Actually, it's more than all there
-is to it, since we've done a few nice things here for the sake
+is to it, because we've done a few nice things here for the sake
of completeness, robustness, and general aesthetics. Simpler
TIESCALAR classes are certainly possible.
for all accesses, even though the constructors differ in names (TIESCALAR
vs TIEARRAY). While in theory you could have the same class servicing
several tied types, in practice this becomes cumbersome, and it's easiest
-to simply keep them at one tie type per class.
+to keep them at simply one tie type per class.
=item STORE this, index, value
=item DESTROY this
This method will be triggered when the tied variable needs to be destructed.
-As with the sclar tie class, this is almost never needed in a
+As with the scalar tie class, this is almost never needed in a
language that does its own garbage collection, so this time we'll
just leave it out.
functions to iterate over all the keys. And DESTROY is called when the
tied variable is garbage collected.
-If this seems like a lot, then feel free to merely inherit
-from the standard Tie::Hash module for most of your methods, redefining only
+If this seems like a lot, then feel free to inherit from
+merely the standard Tie::Hash module for most of your methods, redefining only
the interesting ones. See L<Tie::Hash> for details.
Remember that Perl distinguishes between a key not existing in the hash,
C<defined()> functions.
Here's an example of a somewhat interesting tied hash class: it gives you
-a hash representing a particular user's dotfiles. You index into the hash
-with the name of the file (minus the dot) and you get back that dotfile's
+a hash representing a particular user's dot files. You index into the hash
+with the name of the file (minus the dot) and you get back that dot file's
contents. For example:
use DotFiles;
$dot{login} =~ /MANPATH/ ||
$dot{cshrc} =~ /MANPATH/ )
{
- print "you seem to set your manpath\n";
+ print "you seem to set your MANPATH\n";
}
Or here's another sample of using our tied class:
=item HOME
-where those dotfiles live
+where those dot files live
=item CLOBBER
=item LIST
-the hash of dotfile names and content mappings
+the hash of dot file names and content mappings
=back
my $DEBUG = 0;
sub debug { $DEBUG = @_ ? shift : 1 }
-For our example, we want to able to emit debugging info to help in tracing
+For our example, we want to be able to emit debugging info to help in tracing
during development. We keep also one convenience function around
internally to help print out warnings; whowasi() returns the function name
that calls it.
It's probably worth mentioning that if you're going to filetest the
return values out of a readdir, you'd better prepend the directory
-in question. Otherwise, since we didn't chdir() there, it would
+in question. Otherwise, because we didn't chdir() there, it would
have been testing the wrong file.
=item FETCH this, key
It was easy to write by having it call the Unix cat(1) command, but it
would probably be more portable to open the file manually (and somewhat
-more efficient). Of course, since dot files are a Unixy concept, we're
+more efficient). Of course, because dot files are a Unixy concept, we're
not that concerned.
=item STORE this, key, value
This method is triggered when the whole hash is to be cleared, usually by
assigning the empty list to it.
-In our example, that would remove all the user's dotfiles! It's such a
+In our example, that would remove all the user's dot files! It's such a
dangerous thing that they'll have to set CLOBBER to something higher than
1 to make it happen.
sub CLEAR {
carp &whowasi if $DEBUG;
my $self = shift;
- croak "@{[&whowasi]}: won't remove all dotfiles for $self->{USER}"
+ croak "@{[&whowasi]}: won't remove all dot files for $self->{USER}"
unless $self->{CLOBBER} > 1;
my $dot;
foreach $dot ( keys %{$self->{LIST}}) {
useful if you're carrying about ordering or calling the iterator from more
than one sequence, or not really storing things in a hash anywhere.
-For our example, we our using a real hash so we'll just do the simple
-thing, but we'll have to indirect through the LIST field.
+For our example, we're using a real hash so we'll do just the simple
+thing, but we'll have to go through the LIST field indirectly.
sub NEXTKEY {
carp &whowasi if $DEBUG;
=head2 Tying FileHandles
-This is partially implemeted now.
+This is partially implemented now.
-A class implementing a tied scalar should define the folowing methods:
-TIEHANDLE, PRINT, and possibly DESTROY.
-
-In future READLINE, EOF and possibly others will be added.
+A class implementing a tied filehandle should define the following methods:
+TIEHANDLE, PRINT and/or READLINE, and possibly DESTROY.
It is especially useful when perl is embedded in some other program,
where output to STDOUT and STDERR may have to be redirected in some
=item TIEHANDLE classname, LIST
This is the constructor for the class. That means it is expected to
-return a blessed reference of some sort. The refence can be used to
-hold some internal information. We won't use it in out example.
+return a blessed reference of some sort. The reference can be used to
+hold some internal information.
- sub TIEHANDLE { print "<shout>\n"; bless [], shift }
+ sub TIEHANDLE { print "<shout>\n"; my $i; bless \$i, shift }
=item PRINT this, LIST
This method will be triggered every time the tied handle is printed to.
-Beyond its self refence it also expects the list that was passed to
+Beyond its self reference it also expects the list that was passed to
the print function.
- sub PRINT { shift; for (@_) { print uc($_) } }
+ sub PRINT { $r = shift; $$r++; print join($,,map(uc($_),@_)),$\ }
+
+=item READLINE this
+
+This method will be called when the handle is read from. The method
+should return undef when there is no more data.
+
+ sub READLINE { $r = shift; "PRINT called $$r times\n"; }
=item DESTROY this
print FOO "hello\n";
$a = 4; $b = 6;
print FOO $a, " plus ", $b, " equals ", $a + $b, "\n";
+ print <FOO>;
=head1 SEE ALSO
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 experimental
-module that does attempt to partially address this need is the MLDBM
+module that does attempt to address this need partially is the MLDBM
module. Check your nearest CPAN site as described in L<perlmod> for
source code to MLDBM.
Tom Christiansen
-TIEHANDLE by Sven Verdoolaege <skimo@dns.ufsia.ac.be>
+TIEHANDLE by Sven Verdoolaege E<lt>F<skimo@dns.ufsia.ac.be>E<gt>
https://perl5.git.perl.org / perl5.git / blobdiff