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920dae64 AT |
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; |