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.\" Automatically generated by Pod::Man 2.25 (Pod::Simple 3.20) .\" .\" Standard preamble: .\" ======================================================================== .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left .\" double quote, and \*(R" will give a right double quote. \*(C+ will .\" give a nicer C++. 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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" Tie::Hash, Tie::StdHash, Tie::ExtraHash \- base class definitions for tied hashes .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 2 \& package NewHash; \& require Tie::Hash; \& \& @ISA = qw(Tie::Hash); \& \& sub DELETE { ... } # Provides needed method \& sub CLEAR { ... } # Overrides inherited method \& \& \& package NewStdHash; \& require Tie::Hash; \& \& @ISA = qw(Tie::StdHash); \& \& # All methods provided by default, define only those needing overrides \& # Accessors access the storage in %{$_[0]}; \& # TIEHASH should return a reference to the actual storage \& sub DELETE { ... } \& \& package NewExtraHash; \& require Tie::Hash; \& \& @ISA = qw(Tie::ExtraHash); \& \& # All methods provided by default, define only those needing overrides \& # Accessors access the storage in %{$_[0][0]}; \& # TIEHASH should return an array reference with the first element being \& # the reference to the actual storage \& sub DELETE { \& $_[0][1]\->(\*(Aqdel\*(Aq, $_[0][0], $_[1]); # Call the report writer \& delete $_[0][0]\->{$_[1]}; # $_[0]\->SUPER::DELETE($_[1]) \& } \& \& \& package main; \& \& tie %new_hash, \*(AqNewHash\*(Aq; \& tie %new_std_hash, \*(AqNewStdHash\*(Aq; \& tie %new_extra_hash, \*(AqNewExtraHash\*(Aq, \& sub {warn "Doing \eU$_[1]\eE of $_[2].\en"}; .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" This module provides some skeletal methods for hash-tying classes. See perltie for a list of the functions required in order to tie a hash to a package. The basic \fBTie::Hash\fR package provides a \f(CW\*(C`new\*(C'\fR method, as well as methods \f(CW\*(C`TIEHASH\*(C'\fR, \f(CW\*(C`EXISTS\*(C'\fR and \f(CW\*(C`CLEAR\*(C'\fR. The \fBTie::StdHash\fR and \&\fBTie::ExtraHash\fR packages provide most methods for hashes described in perltie (the exceptions are \f(CW\*(C`UNTIE\*(C'\fR and \f(CW\*(C`DESTROY\*(C'\fR). They cause tied hashes to behave exactly like standard hashes, and allow for selective overwriting of methods. \fBTie::Hash\fR grandfathers the \&\f(CW\*(C`new\*(C'\fR method: it is used if \f(CW\*(C`TIEHASH\*(C'\fR is not defined in the case a class forgets to include a \f(CW\*(C`TIEHASH\*(C'\fR method. .PP For developers wishing to write their own tied hashes, the required methods are briefly defined below. See the perltie section for more detailed descriptive, as well as example code: .IP "\s-1TIEHASH\s0 classname, \s-1LIST\s0" 4 .IX Item "TIEHASH classname, LIST" The method invoked by the command \f(CW\*(C`tie %hash, classname\*(C'\fR. Associates a new hash instance with the specified class. \f(CW\*(C`LIST\*(C'\fR would represent additional arguments (along the lines of AnyDBM_File and compatriots) needed to complete the association. .IP "\s-1STORE\s0 this, key, value" 4 .IX Item "STORE this, key, value" Store datum \fIvalue\fR into \fIkey\fR for the tied hash \fIthis\fR. .IP "\s-1FETCH\s0 this, key" 4 .IX Item "FETCH this, key" Retrieve the datum in \fIkey\fR for the tied hash \fIthis\fR. .IP "\s-1FIRSTKEY\s0 this" 4 .IX Item "FIRSTKEY this" Return the first key in the hash. .IP "\s-1NEXTKEY\s0 this, lastkey" 4 .IX Item "NEXTKEY this, lastkey" Return the next key in the hash. .IP "\s-1EXISTS\s0 this, key" 4 .IX Item "EXISTS this, key" Verify that \fIkey\fR exists with the tied hash \fIthis\fR. .Sp The \fBTie::Hash\fR implementation is a stub that simply croaks. .IP "\s-1DELETE\s0 this, key" 4 .IX Item "DELETE this, key" Delete the key \fIkey\fR from the tied hash \fIthis\fR. .IP "\s-1CLEAR\s0 this" 4 .IX Item "CLEAR this" Clear all values from the tied hash \fIthis\fR. .IP "\s-1SCALAR\s0 this" 4 .IX Item "SCALAR this" Returns what evaluating the hash in scalar context yields. .Sp \&\fBTie::Hash\fR does not implement this method (but \fBTie::StdHash\fR and \fBTie::ExtraHash\fR do). .SH "Inheriting from \fBTie::StdHash\fP" .IX Header "Inheriting from Tie::StdHash" The accessor methods assume that the actual storage for the data in the tied hash is in the hash referenced by \f(CW\*(C`tied(%tiedhash)\*(C'\fR. Thus overwritten \&\f(CW\*(C`TIEHASH\*(C'\fR method should return a hash reference, and the remaining methods should operate on the hash referenced by the first argument: .PP .Vb 2 \& package ReportHash; \& our @ISA = \*(AqTie::StdHash\*(Aq; \& \& sub TIEHASH { \& my $storage = bless {}, shift; \& warn "New ReportHash created, stored in $storage.\en"; \& $storage \& } \& sub STORE { \& warn "Storing data with key $_[1] at $_[0].\en"; \& $_[0]{$_[1]} = $_[2] \& } .Ve .SH "Inheriting from \fBTie::ExtraHash\fP" .IX Header "Inheriting from Tie::ExtraHash" The accessor methods assume that the actual storage for the data in the tied hash is in the hash referenced by \f(CW\*(C`(tied(%tiedhash))\->[0]\*(C'\fR. Thus overwritten \&\f(CW\*(C`TIEHASH\*(C'\fR method should return an array reference with the first element being a hash reference, and the remaining methods should operate on the hash \f(CW\*(C`%{ $_[0]\->[0] }\*(C'\fR: .PP .Vb 2 \& package ReportHash; \& our @ISA = \*(AqTie::ExtraHash\*(Aq; \& \& sub TIEHASH { \& my $class = shift; \& my $storage = bless [{}, @_], $class; \& warn "New ReportHash created, stored in $storage.\en"; \& $storage; \& } \& sub STORE { \& warn "Storing data with key $_[1] at $_[0].\en"; \& $_[0][0]{$_[1]} = $_[2] \& } .Ve .PP The default \f(CW\*(C`TIEHASH\*(C'\fR method stores \*(L"extra\*(R" arguments to \fItie()\fR starting from offset 1 in the array referenced by \f(CW\*(C`tied(%tiedhash)\*(C'\fR; this is the same storage algorithm as in \s-1TIEHASH\s0 subroutine above. Hence, a typical package inheriting from \fBTie::ExtraHash\fR does not need to overwrite this method. .ie n .SH """SCALAR"", ""UNTIE"" and ""DESTROY""" .el .SH "\f(CWSCALAR\fP, \f(CWUNTIE\fP and \f(CWDESTROY\fP" .IX Header "SCALAR, UNTIE and DESTROY" The methods \f(CW\*(C`UNTIE\*(C'\fR and \f(CW\*(C`DESTROY\*(C'\fR are not defined in \fBTie::Hash\fR, \&\fBTie::StdHash\fR, or \fBTie::ExtraHash\fR. Tied hashes do not require presence of these methods, but if defined, the methods will be called in proper time, see perltie. .PP \&\f(CW\*(C`SCALAR\*(C'\fR is only defined in \fBTie::StdHash\fR and \fBTie::ExtraHash\fR. .PP If needed, these methods should be defined by the package inheriting from \&\fBTie::Hash\fR, \fBTie::StdHash\fR, or \fBTie::ExtraHash\fR. See \*(L"\s-1SCALAR\s0\*(R" in perltie to find out what happens when \f(CW\*(C`SCALAR\*(C'\fR does not exist. .SH "MORE INFORMATION" .IX Header "MORE INFORMATION" The packages relating to various DBM-related implementations (\fIDB_File\fR, \&\fINDBM_File\fR, etc.) show examples of general tied hashes, as does the Config module. While these do not utilize \fBTie::Hash\fR, they serve as good working examples.