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86530b38 AT |
1 | package Tie::Hash; |
2 | ||
3 | our $VERSION = '1.00'; | |
4 | ||
5 | =head1 NAME | |
6 | ||
7 | Tie::Hash, Tie::StdHash, Tie::ExtraHash - base class definitions for tied hashes | |
8 | ||
9 | =head1 SYNOPSIS | |
10 | ||
11 | package NewHash; | |
12 | require Tie::Hash; | |
13 | ||
14 | @ISA = (Tie::Hash); | |
15 | ||
16 | sub DELETE { ... } # Provides needed method | |
17 | sub CLEAR { ... } # Overrides inherited method | |
18 | ||
19 | ||
20 | package NewStdHash; | |
21 | require Tie::Hash; | |
22 | ||
23 | @ISA = (Tie::StdHash); | |
24 | ||
25 | # All methods provided by default, define only those needing overrides | |
26 | # Accessors access the storage in %{$_[0]}; | |
27 | # TIEHANDLE 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 | # TIEHANDLE 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 | package main; | |
45 | ||
46 | tie %new_hash, 'NewHash'; | |
47 | tie %new_std_hash, 'NewStdHash'; | |
48 | tie %new_extra_hash, 'NewExtraHash', | |
49 | sub {warn "Doing \U$_[1]\E of $_[2].\n"}; | |
50 | ||
51 | =head1 DESCRIPTION | |
52 | ||
53 | This module provides some skeletal methods for hash-tying classes. See | |
54 | L<perltie> for a list of the functions required in order to tie a hash | |
55 | to a package. The basic B<Tie::Hash> package provides a C<new> method, as well | |
56 | as methods C<TIEHASH>, C<EXISTS> and C<CLEAR>. The B<Tie::StdHash> and | |
57 | B<Tie::ExtraHash> packages | |
58 | provide most methods for hashes described in L<perltie> (the exceptions | |
59 | are C<UNTIE> and C<DESTROY>). They cause tied hashes to behave exactly like standard hashes, | |
60 | and allow for selective overwriting of methods. B<Tie::Hash> grandfathers the | |
61 | C<new> method: it is used if C<TIEHASH> is not defined | |
62 | in the case a class forgets to include a C<TIEHASH> method. | |
63 | ||
64 | For developers wishing to write their own tied hashes, the required methods | |
65 | are briefly defined below. See the L<perltie> section for more detailed | |
66 | descriptive, as well as example code: | |
67 | ||
68 | =over 4 | |
69 | ||
70 | =item TIEHASH classname, LIST | |
71 | ||
72 | The method invoked by the command C<tie %hash, classname>. Associates a new | |
73 | hash instance with the specified class. C<LIST> would represent additional | |
74 | arguments (along the lines of L<AnyDBM_File> and compatriots) needed to | |
75 | complete the association. | |
76 | ||
77 | =item STORE this, key, value | |
78 | ||
79 | Store datum I<value> into I<key> for the tied hash I<this>. | |
80 | ||
81 | =item FETCH this, key | |
82 | ||
83 | Retrieve the datum in I<key> for the tied hash I<this>. | |
84 | ||
85 | =item FIRSTKEY this | |
86 | ||
87 | Return the first key in the hash. | |
88 | ||
89 | =item NEXTKEY this, lastkey | |
90 | ||
91 | Return the next key in the hash. | |
92 | ||
93 | =item EXISTS this, key | |
94 | ||
95 | Verify that I<key> exists with the tied hash I<this>. | |
96 | ||
97 | The B<Tie::Hash> implementation is a stub that simply croaks. | |
98 | ||
99 | =item DELETE this, key | |
100 | ||
101 | Delete the key I<key> from the tied hash I<this>. | |
102 | ||
103 | =item CLEAR this | |
104 | ||
105 | Clear all values from the tied hash I<this>. | |
106 | ||
107 | =back | |
108 | ||
109 | =head1 Inheriting from B<Tie::StdHash> | |
110 | ||
111 | The accessor methods assume that the actual storage for the data in the tied | |
112 | hash is in the hash referenced by C<tied(%tiedhash)>. Thus overwritten | |
113 | C<TIEHANDLE> method should return a hash reference, and the remaining methods | |
114 | should operate on the hash referenced by the first argument: | |
115 | ||
116 | package ReportHash; | |
117 | our @ISA = 'Tie::StdHash'; | |
118 | ||
119 | sub TIEHASH { | |
120 | my $storage = bless {}, shift; | |
121 | warn "New ReportHash created, stored in $storage.\n"; | |
122 | $storage | |
123 | } | |
124 | sub STORE { | |
125 | warn "Storing data with key $_[1] at $_[0].\n"; | |
126 | $_[0]{$_[1]} = $_[2] | |
127 | } | |
128 | ||
129 | ||
130 | =head1 Inheriting from B<Tie::ExtraHash> | |
131 | ||
132 | The accessor methods assume that the actual storage for the data in the tied | |
133 | hash is in the hash referenced by C<(tied(%tiedhash))[0]>. Thus overwritten | |
134 | C<TIEHANDLE> method should return an array reference with the first | |
135 | element being a hash reference, and the remaining methods should operate on the | |
136 | hash C<< %{ $_[0]->[0] } >>: | |
137 | ||
138 | package ReportHash; | |
139 | our @ISA = 'Tie::StdHash'; | |
140 | ||
141 | sub TIEHASH { | |
142 | my $storage = bless {}, shift; | |
143 | warn "New ReportHash created, stored in $storage.\n"; | |
144 | [$storage, @_] | |
145 | } | |
146 | sub STORE { | |
147 | warn "Storing data with key $_[1] at $_[0].\n"; | |
148 | $_[0][0]{$_[1]} = $_[2] | |
149 | } | |
150 | ||
151 | The default C<TIEHANDLE> method stores "extra" arguments to tie() starting | |
152 | from offset 1 in the array referenced by C<tied(%tiedhash)>; this is the | |
153 | same storage algorithm as in TIEHASH subroutine above. Hence, a typical | |
154 | package inheriting from B<Tie::ExtraHash> does not need to overwrite this | |
155 | method. | |
156 | ||
157 | =head1 C<UNTIE> and C<DESTROY> | |
158 | ||
159 | The methods C<UNTIE> and C<DESTROY> are not defined in B<Tie::Hash>, | |
160 | B<Tie::StdHash>, or B<Tie::ExtraHash>. Tied hashes do not require | |
161 | presense of these methods, but if defined, the methods will be called in | |
162 | proper time, see L<perltie>. | |
163 | ||
164 | If needed, these methods should be defined by the package inheriting from | |
165 | B<Tie::Hash>, B<Tie::StdHash>, or B<Tie::ExtraHash>. | |
166 | ||
167 | =head1 MORE INFORMATION | |
168 | ||
169 | The packages relating to various DBM-related implementations (F<DB_File>, | |
170 | F<NDBM_File>, etc.) show examples of general tied hashes, as does the | |
171 | L<Config> module. While these do not utilize B<Tie::Hash>, they serve as | |
172 | good working examples. | |
173 | ||
174 | =cut | |
175 | ||
176 | use Carp; | |
177 | use warnings::register; | |
178 | ||
179 | sub new { | |
180 | my $pkg = shift; | |
181 | $pkg->TIEHASH(@_); | |
182 | } | |
183 | ||
184 | # Grandfather "new" | |
185 | ||
186 | sub TIEHASH { | |
187 | my $pkg = shift; | |
188 | if (defined &{"${pkg}::new"}) { | |
189 | warnings::warnif("WARNING: calling ${pkg}->new since ${pkg}->TIEHASH is missing"); | |
190 | $pkg->new(@_); | |
191 | } | |
192 | else { | |
193 | croak "$pkg doesn't define a TIEHASH method"; | |
194 | } | |
195 | } | |
196 | ||
197 | sub EXISTS { | |
198 | my $pkg = ref $_[0]; | |
199 | croak "$pkg doesn't define an EXISTS method"; | |
200 | } | |
201 | ||
202 | sub CLEAR { | |
203 | my $self = shift; | |
204 | my $key = $self->FIRSTKEY(@_); | |
205 | my @keys; | |
206 | ||
207 | while (defined $key) { | |
208 | push @keys, $key; | |
209 | $key = $self->NEXTKEY(@_, $key); | |
210 | } | |
211 | foreach $key (@keys) { | |
212 | $self->DELETE(@_, $key); | |
213 | } | |
214 | } | |
215 | ||
216 | # The Tie::StdHash package implements standard perl hash behaviour. | |
217 | # It exists to act as a base class for classes which only wish to | |
218 | # alter some parts of their behaviour. | |
219 | ||
220 | package Tie::StdHash; | |
221 | # @ISA = qw(Tie::Hash); # would inherit new() only | |
222 | ||
223 | sub TIEHASH { bless {}, $_[0] } | |
224 | sub STORE { $_[0]->{$_[1]} = $_[2] } | |
225 | sub FETCH { $_[0]->{$_[1]} } | |
226 | sub FIRSTKEY { my $a = scalar keys %{$_[0]}; each %{$_[0]} } | |
227 | sub NEXTKEY { each %{$_[0]} } | |
228 | sub EXISTS { exists $_[0]->{$_[1]} } | |
229 | sub DELETE { delete $_[0]->{$_[1]} } | |
230 | sub CLEAR { %{$_[0]} = () } | |
231 | ||
232 | package Tie::ExtraHash; | |
233 | ||
234 | sub TIEHASH { my $p = shift; bless [{}, @_], $p } | |
235 | sub STORE { $_[0][0]{$_[1]} = $_[2] } | |
236 | sub FETCH { $_[0][0]{$_[1]} } | |
237 | sub FIRSTKEY { my $a = scalar keys %{$_[0][0]}; each %{$_[0][0]} } | |
238 | sub NEXTKEY { each %{$_[0][0]} } | |
239 | sub EXISTS { exists $_[0][0]->{$_[1]} } | |
240 | sub DELETE { delete $_[0][0]->{$_[1]} } | |
241 | sub CLEAR { %{$_[0][0]} = () } | |
242 | ||
243 | 1; |