| 1 | package Tie::Hash; |
| 2 | |
| 3 | our $VERSION = '1.02'; |
| 4 | |
| 5 | =head1 NAME |
| 6 | |
| 7 | Tie::Hash, Tie::StdHash, Tie::ExtraHash - base class definitions for tied hashes |
| 8 | |
| 9 | =head1 SYNOPSIS |
| 10 | |
| 11 | package NewHash; |
| 12 | require Tie::Hash; |
| 13 | |
| 14 | @ISA = (Tie::Hash); |
| 15 | |
| 16 | sub DELETE { ... } # Provides needed method |
| 17 | sub CLEAR { ... } # Overrides inherited method |
| 18 | |
| 19 | |
| 20 | package NewStdHash; |
| 21 | require Tie::Hash; |
| 22 | |
| 23 | @ISA = (Tie::StdHash); |
| 24 | |
| 25 | # All methods provided by default, define only those needing overrides |
| 26 | # Accessors access the storage in %{$_[0]}; |
| 27 | # TIEHASH should return a reference to the actual storage |
| 28 | sub DELETE { ... } |
| 29 | |
| 30 | package NewExtraHash; |
| 31 | require Tie::Hash; |
| 32 | |
| 33 | @ISA = (Tie::ExtraHash); |
| 34 | |
| 35 | # All methods provided by default, define only those needing overrides |
| 36 | # Accessors access the storage in %{$_[0][0]}; |
| 37 | # TIEHASH should return an array reference with the first element being |
| 38 | # the reference to the actual storage |
| 39 | sub DELETE { |
| 40 | $_[0][1]->('del', $_[0][0], $_[1]); # Call the report writer |
| 41 | delete $_[0][0]->{$_[1]}; # $_[0]->SUPER::DELETE($_[1]) |
| 42 | } |
| 43 | |
| 44 | |
| 45 | package main; |
| 46 | |
| 47 | tie %new_hash, 'NewHash'; |
| 48 | tie %new_std_hash, 'NewStdHash'; |
| 49 | tie %new_extra_hash, 'NewExtraHash', |
| 50 | sub {warn "Doing \U$_[1]\E of $_[2].\n"}; |
| 51 | |
| 52 | =head1 DESCRIPTION |
| 53 | |
| 54 | This module provides some skeletal methods for hash-tying classes. See |
| 55 | L<perltie> for a list of the functions required in order to tie a hash |
| 56 | to a package. The basic B<Tie::Hash> package provides a C<new> method, as well |
| 57 | as methods C<TIEHASH>, C<EXISTS> and C<CLEAR>. The B<Tie::StdHash> and |
| 58 | B<Tie::ExtraHash> packages |
| 59 | provide most methods for hashes described in L<perltie> (the exceptions |
| 60 | are C<UNTIE> and C<DESTROY>). They cause tied hashes to behave exactly like standard hashes, |
| 61 | and allow for selective overwriting of methods. B<Tie::Hash> grandfathers the |
| 62 | C<new> method: it is used if C<TIEHASH> is not defined |
| 63 | in the case a class forgets to include a C<TIEHASH> method. |
| 64 | |
| 65 | For developers wishing to write their own tied hashes, the required methods |
| 66 | are briefly defined below. See the L<perltie> section for more detailed |
| 67 | descriptive, as well as example code: |
| 68 | |
| 69 | =over 4 |
| 70 | |
| 71 | =item TIEHASH classname, LIST |
| 72 | |
| 73 | The method invoked by the command C<tie %hash, classname>. Associates a new |
| 74 | hash instance with the specified class. C<LIST> would represent additional |
| 75 | arguments (along the lines of L<AnyDBM_File> and compatriots) needed to |
| 76 | complete the association. |
| 77 | |
| 78 | =item STORE this, key, value |
| 79 | |
| 80 | Store datum I<value> into I<key> for the tied hash I<this>. |
| 81 | |
| 82 | =item FETCH this, key |
| 83 | |
| 84 | Retrieve the datum in I<key> for the tied hash I<this>. |
| 85 | |
| 86 | =item FIRSTKEY this |
| 87 | |
| 88 | Return the first key in the hash. |
| 89 | |
| 90 | =item NEXTKEY this, lastkey |
| 91 | |
| 92 | Return the next key in the hash. |
| 93 | |
| 94 | =item EXISTS this, key |
| 95 | |
| 96 | Verify that I<key> exists with the tied hash I<this>. |
| 97 | |
| 98 | The B<Tie::Hash> implementation is a stub that simply croaks. |
| 99 | |
| 100 | =item DELETE this, key |
| 101 | |
| 102 | Delete the key I<key> from the tied hash I<this>. |
| 103 | |
| 104 | =item CLEAR this |
| 105 | |
| 106 | Clear all values from the tied hash I<this>. |
| 107 | |
| 108 | =item SCALAR this |
| 109 | |
| 110 | Returns what evaluating the hash in scalar context yields. |
| 111 | |
| 112 | B<Tie::Hash> does not implement this method (but B<Tie::StdHash> |
| 113 | and B<Tie::ExtraHash> do). |
| 114 | |
| 115 | =back |
| 116 | |
| 117 | =head1 Inheriting from B<Tie::StdHash> |
| 118 | |
| 119 | The accessor methods assume that the actual storage for the data in the tied |
| 120 | hash is in the hash referenced by C<tied(%tiedhash)>. Thus overwritten |
| 121 | C<TIEHASH> method should return a hash reference, and the remaining methods |
| 122 | should operate on the hash referenced by the first argument: |
| 123 | |
| 124 | package ReportHash; |
| 125 | our @ISA = 'Tie::StdHash'; |
| 126 | |
| 127 | sub TIEHASH { |
| 128 | my $storage = bless {}, shift; |
| 129 | warn "New ReportHash created, stored in $storage.\n"; |
| 130 | $storage |
| 131 | } |
| 132 | sub STORE { |
| 133 | warn "Storing data with key $_[1] at $_[0].\n"; |
| 134 | $_[0]{$_[1]} = $_[2] |
| 135 | } |
| 136 | |
| 137 | |
| 138 | =head1 Inheriting from B<Tie::ExtraHash> |
| 139 | |
| 140 | The accessor methods assume that the actual storage for the data in the tied |
| 141 | hash is in the hash referenced by C<(tied(%tiedhash))-E<gt>[0]>. Thus overwritten |
| 142 | C<TIEHASH> method should return an array reference with the first |
| 143 | element being a hash reference, and the remaining methods should operate on the |
| 144 | hash C<< %{ $_[0]->[0] } >>: |
| 145 | |
| 146 | package ReportHash; |
| 147 | our @ISA = 'Tie::ExtraHash'; |
| 148 | |
| 149 | sub TIEHASH { |
| 150 | my $class = shift; |
| 151 | my $storage = bless [{}, @_], $class; |
| 152 | warn "New ReportHash created, stored in $storage.\n"; |
| 153 | $storage; |
| 154 | } |
| 155 | sub STORE { |
| 156 | warn "Storing data with key $_[1] at $_[0].\n"; |
| 157 | $_[0][0]{$_[1]} = $_[2] |
| 158 | } |
| 159 | |
| 160 | The default C<TIEHASH> method stores "extra" arguments to tie() starting |
| 161 | from offset 1 in the array referenced by C<tied(%tiedhash)>; this is the |
| 162 | same storage algorithm as in TIEHASH subroutine above. Hence, a typical |
| 163 | package inheriting from B<Tie::ExtraHash> does not need to overwrite this |
| 164 | method. |
| 165 | |
| 166 | =head1 C<SCALAR>, C<UNTIE> and C<DESTROY> |
| 167 | |
| 168 | The methods C<UNTIE> and C<DESTROY> are not defined in B<Tie::Hash>, |
| 169 | B<Tie::StdHash>, or B<Tie::ExtraHash>. Tied hashes do not require |
| 170 | presence of these methods, but if defined, the methods will be called in |
| 171 | proper time, see L<perltie>. |
| 172 | |
| 173 | C<SCALAR> is only defined in B<Tie::StdHash> and B<Tie::ExtraHash>. |
| 174 | |
| 175 | If needed, these methods should be defined by the package inheriting from |
| 176 | B<Tie::Hash>, B<Tie::StdHash>, or B<Tie::ExtraHash>. See L<pertie/"SCALAR"> |
| 177 | to find out what happens when C<SCALAR> does not exist. |
| 178 | |
| 179 | =head1 MORE INFORMATION |
| 180 | |
| 181 | The packages relating to various DBM-related implementations (F<DB_File>, |
| 182 | F<NDBM_File>, etc.) show examples of general tied hashes, as does the |
| 183 | L<Config> module. While these do not utilize B<Tie::Hash>, they serve as |
| 184 | good working examples. |
| 185 | |
| 186 | =cut |
| 187 | |
| 188 | use Carp; |
| 189 | use warnings::register; |
| 190 | |
| 191 | sub new { |
| 192 | my $pkg = shift; |
| 193 | $pkg->TIEHASH(@_); |
| 194 | } |
| 195 | |
| 196 | # Grandfather "new" |
| 197 | |
| 198 | sub TIEHASH { |
| 199 | my $pkg = shift; |
| 200 | if (defined &{"${pkg}::new"}) { |
| 201 | warnings::warnif("WARNING: calling ${pkg}->new since ${pkg}->TIEHASH is missing"); |
| 202 | $pkg->new(@_); |
| 203 | } |
| 204 | else { |
| 205 | croak "$pkg doesn't define a TIEHASH method"; |
| 206 | } |
| 207 | } |
| 208 | |
| 209 | sub EXISTS { |
| 210 | my $pkg = ref $_[0]; |
| 211 | croak "$pkg doesn't define an EXISTS method"; |
| 212 | } |
| 213 | |
| 214 | sub CLEAR { |
| 215 | my $self = shift; |
| 216 | my $key = $self->FIRSTKEY(@_); |
| 217 | my @keys; |
| 218 | |
| 219 | while (defined $key) { |
| 220 | push @keys, $key; |
| 221 | $key = $self->NEXTKEY(@_, $key); |
| 222 | } |
| 223 | foreach $key (@keys) { |
| 224 | $self->DELETE(@_, $key); |
| 225 | } |
| 226 | } |
| 227 | |
| 228 | # The Tie::StdHash package implements standard perl hash behaviour. |
| 229 | # It exists to act as a base class for classes which only wish to |
| 230 | # alter some parts of their behaviour. |
| 231 | |
| 232 | package Tie::StdHash; |
| 233 | # @ISA = qw(Tie::Hash); # would inherit new() only |
| 234 | |
| 235 | sub TIEHASH { bless {}, $_[0] } |
| 236 | sub STORE { $_[0]->{$_[1]} = $_[2] } |
| 237 | sub FETCH { $_[0]->{$_[1]} } |
| 238 | sub FIRSTKEY { my $a = scalar keys %{$_[0]}; each %{$_[0]} } |
| 239 | sub NEXTKEY { each %{$_[0]} } |
| 240 | sub EXISTS { exists $_[0]->{$_[1]} } |
| 241 | sub DELETE { delete $_[0]->{$_[1]} } |
| 242 | sub CLEAR { %{$_[0]} = () } |
| 243 | sub SCALAR { scalar %{$_[0]} } |
| 244 | |
| 245 | package Tie::ExtraHash; |
| 246 | |
| 247 | sub TIEHASH { my $p = shift; bless [{}, @_], $p } |
| 248 | sub STORE { $_[0][0]{$_[1]} = $_[2] } |
| 249 | sub FETCH { $_[0][0]{$_[1]} } |
| 250 | sub FIRSTKEY { my $a = scalar keys %{$_[0][0]}; each %{$_[0][0]} } |
| 251 | sub NEXTKEY { each %{$_[0][0]} } |
| 252 | sub EXISTS { exists $_[0][0]->{$_[1]} } |
| 253 | sub DELETE { delete $_[0][0]->{$_[1]} } |
| 254 | sub CLEAR { %{$_[0][0]} = () } |
| 255 | sub SCALAR { scalar %{$_[0][0]} } |
| 256 | |
| 257 | 1; |