tieVARIABLE
,CLASSNAME
,LIST
This function binds a variable to a package class that will provide
the implementation for the variable. VARIABLE
is the name of the
variable to be tied. CLASSNAME
is the name of a class
implementing objects of an appropriate type. Any additional arguments are
passed to the "new" method of the class (meaning TIESCALAR
,
TIEARRAY
, or TIEHASH
). Typically these are arguments such
as might be passed to the dbm_open(3) function of C, but this is
package dependent. The object
returned by the "new" method is also returned by the tie
function, which can be useful if you want to access other methods in
CLASSNAME
. (The object can also be accessed through the tied
function.) So, a class for tying a hash to an ISAM implementation
might provide an extra method to traverse a set of keys sequentially
(the "S" of ISAM), since your typical DBM implementation can't do that.
Note that functions such as keys and values may return huge list values when used on large objects like DBM files. You may prefer to use the each function to iterate over such. For example:
use NDBM_File; tie %ALIASES, "NDBM_File", "/etc/aliases", 1, 0 or die "Can't open aliases: $!\n"; while (($key,$val) = each %ALIASES) { print $key, ' = ', $val, "\n"; } untie %ALIASES;
A class implementing a hash should provide the following methods:
TIEHASH $class, LIST
DESTROY $self
FETCH $self, $key
STORE $self, $key, $value
DELETE $self, $key
EXISTS $self, $key
FIRSTKEY $self
NEXTKEY $self, $lastkey
A class implementing an ordinary array should provide the following methods:
TIEARRAY $classname, LIST
DESTROY $self
FETCH $self, $subscript
STORE $self, $subscript, $value
(As of this writing, other methods are still being designed. Check the online documentation for additions.)
A class implementing a scalar should provide the following methods:
TIESCALAR $classname, LIST
DESTROY $self
FETCH $self,
STORE $self, $value
See "Using Tied Variables" in Chapter 5 for detailed discussion of all these methods. Unlike dbmopen, the tie function will not use or require a module for you - you need to do that explicitly yourself. See the DB_File and Config modules for interesting tie implementations.