The tie() function binds a variable to a class (package) that will provide
the implementation for access methods for that variable. Once this magic
has been performed, accessing a tied variable automatically triggers
-method calls in the proper class. All of the complexity of the class is
+method calls in the proper class. The complexity of the class is
hidden behind magic methods calls. The method names are in ALL CAPS,
which is a convention that Perl uses to indicate that they're called
implicitly rather than explicitly--just like the BEGIN() and END()
FETCHSIZE and STORESIZE are used to provide C<$#array> and
equivalent C<scalar(@array)> access.
-
-The methods POP, PUSH, SHIFT, UNSHIFT, SPLICE are required if the perl
-operator with the corresponding (but lowercase) name is to operate on the
-tied array. The B<Tie::Array> class can be used as a base class to implement
-these in terms of the basic five methods above.
+
+The methods POP, PUSH, SHIFT, UNSHIFT, SPLICE, DELETE, and EXISTS are
+required if the perl operator with the corresponding (but lowercase) name
+is to operate on the tied array. The B<Tie::Array> class can be used as a
+base class to implement the first five of these in terms of the basic
+methods above. The default implementations of DELETE and EXISTS in
+B<Tie::Array> simply C<croak>.
In addition EXTEND will be called when perl would have pre-extended
allocation in a real array.
=back
-Note that functions such as keys() and values() may return huge array
-values when used on large objects, like DBM files. You may prefer to
-use the each() function to iterate over such. Example:
+Note that functions such as keys() and values() may return huge lists
+when used on large objects, like DBM files. You may prefer to use the
+each() function to iterate over such. Example:
# print out history file offsets
use NDBM_File;
A class implementing a tied filehandle should define the following
methods: TIEHANDLE, at least one of PRINT, PRINTF, WRITE, READLINE, GETC,
-READ, and possibly CLOSE and DESTROY.
+READ, and possibly CLOSE and DESTROY. The class can also provide: BINMODE,
+OPEN, EOF, FILENO, SEEK, TELL - if the corresponding perl operators are
+used on the handle.
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
or C<sysread> functions.
sub READ {
- $r = shift;
- my($buf,$len,$offset) = @_;
- print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset";
+ my $self = shift;
+ my $$bufref = \$_[0];
+ my(undef,$len,$offset) = @_;
+ print "READ called, \$buf=$bufref, \$len=$len, \$offset=$offset";
+ # add to $$bufref, set $len to number of characters read
+ $len;
}
=item READLINE this
This method will be called when the handle is read from via <HANDLE>.
The method should return undef when there is no more data.
- sub READLINE { $r = shift; "PRINT called $$r times\n"; }
+ sub READLINE { $r = shift; "READLINE called $$r times\n"; }
=item GETC this
package Remember;
use strict;
+ use warnings;
use IO::File;
sub TIESCALAR {
no more valid references; and thus the file is closed.
In the second example, however, we have stored another reference to
-the tied object in C<$x>. That means that when untie() gets called
+the tied object in $x. That means that when untie() gets called
there will still be a valid reference to the object in existence, so
the destructor is not called at that time, and thus the file is not
closed. The reason there is no output is because the file buffers
Now that you know what the problem is, what can you do to avoid it?
Well, the good old C<-w> flag will spot any instances where you call
untie() and there are still valid references to the tied object. If
-the second script above is run with the C<-w> flag, Perl prints this
+the second script above this near the top C<use warnings 'untie'>
+or was run with the C<-w> flag, Perl prints this
warning message:
untie attempted while 1 inner references still exist
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