Commit | Line | Data |
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64d0c973 | 1 | package Tie::Hash; |
cb1a09d0 | 2 | |
98225a64 | 3 | our $VERSION = '1.02'; |
b75c8c73 | 4 | |
cb1a09d0 AD |
5 | =head1 NAME |
6 | ||
d5582e24 | 7 | Tie::Hash, Tie::StdHash, Tie::ExtraHash - base class definitions for tied hashes |
cb1a09d0 AD |
8 | |
9 | =head1 SYNOPSIS | |
10 | ||
11 | package NewHash; | |
64d0c973 | 12 | require Tie::Hash; |
bbc7dcd2 | 13 | |
abc0156b | 14 | @ISA = qw(Tie::Hash); |
bbc7dcd2 | 15 | |
cb1a09d0 AD |
16 | sub DELETE { ... } # Provides needed method |
17 | sub CLEAR { ... } # Overrides inherited method | |
bbc7dcd2 MS |
18 | |
19 | ||
cb1a09d0 | 20 | package NewStdHash; |
64d0c973 | 21 | require Tie::Hash; |
bbc7dcd2 | 22 | |
abc0156b | 23 | @ISA = qw(Tie::StdHash); |
bbc7dcd2 | 24 | |
cb1a09d0 | 25 | # All methods provided by default, define only those needing overrides |
d5582e24 | 26 | # Accessors access the storage in %{$_[0]}; |
15634f32 | 27 | # TIEHASH should return a reference to the actual storage |
cb1a09d0 | 28 | sub DELETE { ... } |
bbc7dcd2 | 29 | |
d5582e24 IZ |
30 | package NewExtraHash; |
31 | require Tie::Hash; | |
32 | ||
abc0156b | 33 | @ISA = qw(Tie::ExtraHash); |
d5582e24 IZ |
34 | |
35 | # All methods provided by default, define only those needing overrides | |
36 | # Accessors access the storage in %{$_[0][0]}; | |
15634f32 | 37 | # TIEHASH should return an array reference with the first element being |
d5582e24 IZ |
38 | # the reference to the actual storage |
39 | sub DELETE { | |
40 | $_[0][1]->('del', $_[0][0], $_[1]); # Call the report writer | |
96820f7c SR |
41 | delete $_[0][0]->{$_[1]}; # $_[0]->SUPER::DELETE($_[1]) |
42 | } | |
d5582e24 | 43 | |
bbc7dcd2 | 44 | |
cb1a09d0 | 45 | package main; |
bbc7dcd2 | 46 | |
c954a603 | 47 | tie %new_hash, 'NewHash'; |
48 | tie %new_std_hash, 'NewStdHash'; | |
d5582e24 IZ |
49 | tie %new_extra_hash, 'NewExtraHash', |
50 | sub {warn "Doing \U$_[1]\E of $_[2].\n"}; | |
cb1a09d0 AD |
51 | |
52 | =head1 DESCRIPTION | |
53 | ||
54 | This module provides some skeletal methods for hash-tying classes. See | |
64d0c973 RR |
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 | |
d5582e24 IZ |
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. | |
cb1a09d0 AD |
64 | |
65 | For developers wishing to write their own tied hashes, the required methods | |
64d0c973 RR |
66 | are briefly defined below. See the L<perltie> section for more detailed |
67 | descriptive, as well as example code: | |
68 | ||
bbc7dcd2 | 69 | =over 4 |
cb1a09d0 AD |
70 | |
71 | =item TIEHASH classname, LIST | |
72 | ||
64d0c973 | 73 | The method invoked by the command C<tie %hash, classname>. Associates a new |
cb1a09d0 AD |
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 | ||
51c7a601 | 88 | Return the first key in the hash. |
cb1a09d0 AD |
89 | |
90 | =item NEXTKEY this, lastkey | |
91 | ||
51c7a601 | 92 | Return the next key in the hash. |
cb1a09d0 AD |
93 | |
94 | =item EXISTS this, key | |
95 | ||
96 | Verify that I<key> exists with the tied hash I<this>. | |
97 | ||
01020589 GS |
98 | The B<Tie::Hash> implementation is a stub that simply croaks. |
99 | ||
cb1a09d0 AD |
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 | ||
a3bcc51e TP |
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 | ||
cb1a09d0 AD |
115 | =back |
116 | ||
d5582e24 IZ |
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 | |
15634f32 | 121 | C<TIEHASH> method should return a hash reference, and the remaining methods |
d5582e24 IZ |
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 | ||
cb1a09d0 | 137 | |
d5582e24 IZ |
138 | =head1 Inheriting from B<Tie::ExtraHash> |
139 | ||
140 | The accessor methods assume that the actual storage for the data in the tied | |
a3bcc51e | 141 | hash is in the hash referenced by C<(tied(%tiedhash))-E<gt>[0]>. Thus overwritten |
15634f32 | 142 | C<TIEHASH> method should return an array reference with the first |
d5582e24 | 143 | element being a hash reference, and the remaining methods should operate on the |
194eaab5 | 144 | hash C<< %{ $_[0]->[0] } >>: |
d5582e24 IZ |
145 | |
146 | package ReportHash; | |
1db7d662 | 147 | our @ISA = 'Tie::ExtraHash'; |
d5582e24 IZ |
148 | |
149 | sub TIEHASH { | |
1db7d662 BT |
150 | my $class = shift; |
151 | my $storage = bless [{}, @_], $class; | |
d5582e24 | 152 | warn "New ReportHash created, stored in $storage.\n"; |
1db7d662 | 153 | $storage; |
d5582e24 IZ |
154 | } |
155 | sub STORE { | |
156 | warn "Storing data with key $_[1] at $_[0].\n"; | |
157 | $_[0][0]{$_[1]} = $_[2] | |
158 | } | |
159 | ||
15634f32 | 160 | The default C<TIEHASH> method stores "extra" arguments to tie() starting |
d5582e24 IZ |
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 | ||
a3bcc51e | 166 | =head1 C<SCALAR>, C<UNTIE> and C<DESTROY> |
d5582e24 IZ |
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 | |
3c4b39be | 170 | presence of these methods, but if defined, the methods will be called in |
d5582e24 IZ |
171 | proper time, see L<perltie>. |
172 | ||
a3bcc51e TP |
173 | C<SCALAR> is only defined in B<Tie::StdHash> and B<Tie::ExtraHash>. |
174 | ||
d5582e24 | 175 | If needed, these methods should be defined by the package inheriting from |
a3bcc51e TP |
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. | |
cb1a09d0 AD |
178 | |
179 | =head1 MORE INFORMATION | |
180 | ||
8dcee03e | 181 | The packages relating to various DBM-related implementations (F<DB_File>, |
cb1a09d0 | 182 | F<NDBM_File>, etc.) show examples of general tied hashes, as does the |
64d0c973 | 183 | L<Config> module. While these do not utilize B<Tie::Hash>, they serve as |
cb1a09d0 AD |
184 | good working examples. |
185 | ||
186 | =cut | |
a6006777 | 187 | |
a0d0e21e | 188 | use Carp; |
d3a7d8c7 | 189 | use warnings::register; |
a0d0e21e LW |
190 | |
191 | sub new { | |
4633a7c4 LW |
192 | my $pkg = shift; |
193 | $pkg->TIEHASH(@_); | |
a0d0e21e LW |
194 | } |
195 | ||
196 | # Grandfather "new" | |
197 | ||
198 | sub TIEHASH { | |
4633a7c4 | 199 | my $pkg = shift; |
cc6b7395 | 200 | if (defined &{"${pkg}::new"}) { |
7e6d00f8 | 201 | warnings::warnif("WARNING: calling ${pkg}->new since ${pkg}->TIEHASH is missing"); |
4633a7c4 | 202 | $pkg->new(@_); |
a0d0e21e LW |
203 | } |
204 | else { | |
4633a7c4 | 205 | croak "$pkg doesn't define a TIEHASH method"; |
a0d0e21e LW |
206 | } |
207 | } | |
208 | ||
209 | sub EXISTS { | |
4633a7c4 LW |
210 | my $pkg = ref $_[0]; |
211 | croak "$pkg doesn't define an EXISTS method"; | |
a0d0e21e LW |
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 | ||
64d0c973 | 228 | # The Tie::StdHash package implements standard perl hash behaviour. |
748a9306 LW |
229 | # It exists to act as a base class for classes which only wish to |
230 | # alter some parts of their behaviour. | |
231 | ||
64d0c973 | 232 | package Tie::StdHash; |
d5582e24 | 233 | # @ISA = qw(Tie::Hash); # would inherit new() only |
748a9306 LW |
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 { %{$_[0]} = () } | |
a3bcc51e | 243 | sub SCALAR { scalar %{$_[0]} } |
748a9306 | 244 | |
d5582e24 IZ |
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 { %{$_[0][0]} = () } | |
a3bcc51e | 255 | sub SCALAR { scalar %{$_[0][0]} } |
d5582e24 | 256 | |
a0d0e21e | 257 | 1; |