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1 | package Tie::Hash; |
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2 | |
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3 | our $VERSION = '1.00'; |
4 | |
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5 | =head1 NAME |
6 | |
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7 | Tie::Hash, Tie::StdHash, Tie::ExtraHash - base class definitions for tied hashes |
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8 | |
9 | =head1 SYNOPSIS |
10 | |
11 | package NewHash; |
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12 | require Tie::Hash; |
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13 | |
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14 | @ISA = (Tie::Hash); |
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15 | |
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16 | sub DELETE { ... } # Provides needed method |
17 | sub CLEAR { ... } # Overrides inherited method |
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18 | |
19 | |
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20 | package NewStdHash; |
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21 | require Tie::Hash; |
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22 | |
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23 | @ISA = (Tie::StdHash); |
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24 | |
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25 | # All methods provided by default, define only those needing overrides |
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26 | # Accessors access the storage in %{$_[0]}; |
27 | # TIEHANDLE should return a reference to the actual storage |
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28 | sub DELETE { ... } |
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29 | |
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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 | |
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43 | |
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44 | package main; |
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45 | |
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46 | tie %new_hash, 'NewHash'; |
47 | tie %new_std_hash, 'NewStdHash'; |
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48 | tie %new_extra_hash, 'NewExtraHash', |
49 | sub {warn "Doing \U$_[1]\E of $_[2].\n"}; |
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50 | |
51 | =head1 DESCRIPTION |
52 | |
53 | This module provides some skeletal methods for hash-tying classes. See |
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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 |
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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. |
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63 | |
64 | For developers wishing to write their own tied hashes, the required methods |
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65 | are briefly defined below. See the L<perltie> section for more detailed |
66 | descriptive, as well as example code: |
67 | |
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68 | =over 4 |
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69 | |
70 | =item TIEHASH classname, LIST |
71 | |
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72 | The method invoked by the command C<tie %hash, classname>. Associates a new |
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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 | |
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87 | Return the first key in the hash. |
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88 | |
89 | =item NEXTKEY this, lastkey |
90 | |
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91 | Return the next key in the hash. |
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92 | |
93 | =item EXISTS this, key |
94 | |
95 | Verify that I<key> exists with the tied hash I<this>. |
96 | |
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97 | The B<Tie::Hash> implementation is a stub that simply croaks. |
98 | |
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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 | |
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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 | |
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129 | |
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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 |
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136 | hash C<< %{ $_[0]->[0] } >>: |
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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>. |
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166 | |
167 | =head1 MORE INFORMATION |
168 | |
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169 | The packages relating to various DBM-related implementations (F<DB_File>, |
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170 | F<NDBM_File>, etc.) show examples of general tied hashes, as does the |
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171 | L<Config> module. While these do not utilize B<Tie::Hash>, they serve as |
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172 | good working examples. |
173 | |
174 | =cut |
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175 | |
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176 | use Carp; |
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177 | use warnings::register; |
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178 | |
179 | sub new { |
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180 | my $pkg = shift; |
181 | $pkg->TIEHASH(@_); |
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182 | } |
183 | |
184 | # Grandfather "new" |
185 | |
186 | sub TIEHASH { |
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187 | my $pkg = shift; |
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188 | if (defined &{"${pkg}::new"}) { |
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189 | warnings::warnif("WARNING: calling ${pkg}->new since ${pkg}->TIEHASH is missing"); |
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190 | $pkg->new(@_); |
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191 | } |
192 | else { |
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193 | croak "$pkg doesn't define a TIEHASH method"; |
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194 | } |
195 | } |
196 | |
197 | sub EXISTS { |
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198 | my $pkg = ref $_[0]; |
199 | croak "$pkg doesn't define an EXISTS method"; |
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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 | |
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216 | # The Tie::StdHash package implements standard perl hash behaviour. |
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217 | # It exists to act as a base class for classes which only wish to |
218 | # alter some parts of their behaviour. |
219 | |
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220 | package Tie::StdHash; |
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221 | # @ISA = qw(Tie::Hash); # would inherit new() only |
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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 | |
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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 | |
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243 | 1; |