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1 | package Tie::Hash; |
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2 | |
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3 | our $VERSION = '1.01'; |
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4 | |
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5 | =head1 NAME |
6 | |
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7 | Tie::Hash, Tie::StdHash, Tie::ExtraHash - base class definitions for tied hashes |
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8 | |
9 | =head1 SYNOPSIS |
10 | |
11 | package NewHash; |
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12 | require Tie::Hash; |
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13 | |
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14 | @ISA = (Tie::Hash); |
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15 | |
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16 | sub DELETE { ... } # Provides needed method |
17 | sub CLEAR { ... } # Overrides inherited method |
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18 | |
19 | |
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20 | package NewStdHash; |
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21 | require Tie::Hash; |
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22 | |
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23 | @ISA = (Tie::StdHash); |
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24 | |
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25 | # All methods provided by default, define only those needing overrides |
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26 | # Accessors access the storage in %{$_[0]}; |
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27 | # TIEHASH 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]}; |
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37 | # TIEHASH should return an array reference with the first element being |
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38 | # the reference to the actual storage |
39 | sub DELETE { |
40 | $_[0][1]->('del', $_[0][0], $_[1]); # Call the report writer |
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41 | delete $_[0][0]->{$_[1]}; # $_[0]->SUPER::DELETE($_[1]) |
42 | } |
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43 | |
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44 | |
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45 | package main; |
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46 | |
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47 | tie %new_hash, 'NewHash'; |
48 | tie %new_std_hash, 'NewStdHash'; |
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49 | tie %new_extra_hash, 'NewExtraHash', |
50 | sub {warn "Doing \U$_[1]\E of $_[2].\n"}; |
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51 | |
52 | =head1 DESCRIPTION |
53 | |
54 | This module provides some skeletal methods for hash-tying classes. See |
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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 |
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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. |
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64 | |
65 | For developers wishing to write their own tied hashes, the required methods |
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66 | are briefly defined below. See the L<perltie> section for more detailed |
67 | descriptive, as well as example code: |
68 | |
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69 | =over 4 |
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70 | |
71 | =item TIEHASH classname, LIST |
72 | |
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73 | The method invoked by the command C<tie %hash, classname>. Associates a new |
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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 | |
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88 | Return the first key in the hash. |
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89 | |
90 | =item NEXTKEY this, lastkey |
91 | |
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92 | Return the next key in the hash. |
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93 | |
94 | =item EXISTS this, key |
95 | |
96 | Verify that I<key> exists with the tied hash I<this>. |
97 | |
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98 | The B<Tie::Hash> implementation is a stub that simply croaks. |
99 | |
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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 | |
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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 | |
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115 | =back |
116 | |
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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 |
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121 | C<TIEHASH> method should return a hash reference, and the remaining methods |
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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 | |
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137 | |
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138 | =head1 Inheriting from B<Tie::ExtraHash> |
139 | |
140 | The accessor methods assume that the actual storage for the data in the tied |
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141 | hash is in the hash referenced by C<(tied(%tiedhash))-E<gt>[0]>. Thus overwritten |
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142 | C<TIEHASH> method should return an array reference with the first |
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143 | element being a hash reference, and the remaining methods should operate on the |
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144 | hash C<< %{ $_[0]->[0] } >>: |
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145 | |
146 | package ReportHash; |
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147 | our @ISA = 'Tie::ExtraHash'; |
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148 | |
149 | sub TIEHASH { |
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150 | my $class = shift; |
151 | my $storage = bless [{}, @_], $class; |
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152 | warn "New ReportHash created, stored in $storage.\n"; |
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153 | $storage; |
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154 | } |
155 | sub STORE { |
156 | warn "Storing data with key $_[1] at $_[0].\n"; |
157 | $_[0][0]{$_[1]} = $_[2] |
158 | } |
159 | |
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160 | The default C<TIEHASH> method stores "extra" arguments to tie() starting |
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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 | |
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166 | =head1 C<SCALAR>, C<UNTIE> and C<DESTROY> |
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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 | presense of these methods, but if defined, the methods will be called in |
171 | proper time, see L<perltie>. |
172 | |
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173 | C<SCALAR> is only defined in B<Tie::StdHash> and B<Tie::ExtraHash>. |
174 | |
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175 | If needed, these methods should be defined by the package inheriting from |
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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. |
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178 | |
179 | =head1 MORE INFORMATION |
180 | |
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181 | The packages relating to various DBM-related implementations (F<DB_File>, |
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182 | F<NDBM_File>, etc.) show examples of general tied hashes, as does the |
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183 | L<Config> module. While these do not utilize B<Tie::Hash>, they serve as |
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184 | good working examples. |
185 | |
186 | =cut |
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187 | |
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188 | use Carp; |
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189 | use warnings::register; |
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190 | |
191 | sub new { |
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192 | my $pkg = shift; |
193 | $pkg->TIEHASH(@_); |
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194 | } |
195 | |
196 | # Grandfather "new" |
197 | |
198 | sub TIEHASH { |
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199 | my $pkg = shift; |
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200 | if (defined &{"${pkg}::new"}) { |
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201 | warnings::warnif("WARNING: calling ${pkg}->new since ${pkg}->TIEHASH is missing"); |
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202 | $pkg->new(@_); |
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203 | } |
204 | else { |
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205 | croak "$pkg doesn't define a TIEHASH method"; |
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206 | } |
207 | } |
208 | |
209 | sub EXISTS { |
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210 | my $pkg = ref $_[0]; |
211 | croak "$pkg doesn't define an EXISTS method"; |
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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 | |
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228 | # The Tie::StdHash package implements standard perl hash behaviour. |
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229 | # It exists to act as a base class for classes which only wish to |
230 | # alter some parts of their behaviour. |
231 | |
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232 | package Tie::StdHash; |
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233 | # @ISA = qw(Tie::Hash); # would inherit new() only |
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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 { %{$_[0]} = () } |
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243 | sub SCALAR { scalar %{$_[0]} } |
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244 | |
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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 { %{$_[0][0]} = () } |
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255 | sub SCALAR { scalar %{$_[0][0]} } |
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256 | |
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257 | 1; |