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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "Hash::Util 3" | |
132 | .TH Hash::Util 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | Hash::Util \- A selection of general\-utility hash subroutines | |
135 | .SH "SYNOPSIS" | |
136 | .IX Header "SYNOPSIS" | |
137 | .Vb 4 | |
138 | \& use Hash::Util qw(lock_keys unlock_keys | |
139 | \& lock_value unlock_value | |
140 | \& lock_hash unlock_hash | |
141 | \& hash_seed); | |
142 | .Ve | |
143 | .PP | |
144 | .Vb 4 | |
145 | \& %hash = (foo => 42, bar => 23); | |
146 | \& lock_keys(%hash); | |
147 | \& lock_keys(%hash, @keyset); | |
148 | \& unlock_keys(%hash); | |
149 | .Ve | |
150 | .PP | |
151 | .Vb 2 | |
152 | \& lock_value (%hash, 'foo'); | |
153 | \& unlock_value(%hash, 'foo'); | |
154 | .Ve | |
155 | .PP | |
156 | .Vb 2 | |
157 | \& lock_hash (%hash); | |
158 | \& unlock_hash(%hash); | |
159 | .Ve | |
160 | .PP | |
161 | .Vb 1 | |
162 | \& my $hashes_are_randomised = hash_seed() != 0; | |
163 | .Ve | |
164 | .SH "DESCRIPTION" | |
165 | .IX Header "DESCRIPTION" | |
166 | \&\f(CW\*(C`Hash::Util\*(C'\fR contains special functions for manipulating hashes that | |
167 | don't really warrant a keyword. | |
168 | .PP | |
169 | By default \f(CW\*(C`Hash::Util\*(C'\fR does not export anything. | |
170 | .Sh "Restricted hashes" | |
171 | .IX Subsection "Restricted hashes" | |
172 | 5.8.0 introduces the ability to restrict a hash to a certain set of | |
173 | keys. No keys outside of this set can be added. It also introduces | |
174 | the ability to lock an individual key so it cannot be deleted and the | |
175 | value cannot be changed. | |
176 | .PP | |
177 | This is intended to largely replace the deprecated pseudo\-hashes. | |
178 | .IP "lock_keys" 4 | |
179 | .IX Item "lock_keys" | |
180 | .PD 0 | |
181 | .IP "unlock_keys" 4 | |
182 | .IX Item "unlock_keys" | |
183 | .PD | |
184 | .Vb 2 | |
185 | \& lock_keys(%hash); | |
186 | \& lock_keys(%hash, @keys); | |
187 | .Ve | |
188 | .Sp | |
189 | Restricts the given \f(CW%hash\fR's set of keys to \f(CW@keys\fR. If \f(CW@keys\fR is not | |
190 | given it restricts it to its current keyset. No more keys can be | |
191 | added. \fIdelete()\fR and \fIexists()\fR will still work, but will not alter | |
192 | the set of allowed keys. \fBNote\fR: the current implementation prevents | |
193 | the hash from being \fIbless()\fRed while it is in a locked state. Any attempt | |
194 | to do so will raise an exception. Of course you can still \fIbless()\fR | |
195 | the hash before you call \fIlock_keys()\fR so this shouldn't be a problem. | |
196 | .Sp | |
197 | .Vb 1 | |
198 | \& unlock_keys(%hash); | |
199 | .Ve | |
200 | .Sp | |
201 | Removes the restriction on the \f(CW%hash\fR's keyset. | |
202 | .IP "lock_value" 4 | |
203 | .IX Item "lock_value" | |
204 | .PD 0 | |
205 | .IP "unlock_value" 4 | |
206 | .IX Item "unlock_value" | |
207 | .PD | |
208 | .Vb 2 | |
209 | \& lock_value (%hash, $key); | |
210 | \& unlock_value(%hash, $key); | |
211 | .Ve | |
212 | .Sp | |
213 | Locks and unlocks an individual key of a hash. The value of a locked | |
214 | key cannot be changed. | |
215 | .Sp | |
216 | %hash must have already been locked for this to have useful effect. | |
217 | .IP "\fBlock_hash\fR" 4 | |
218 | .IX Item "lock_hash" | |
219 | .PD 0 | |
220 | .IP "\fBunlock_hash\fR" 4 | |
221 | .IX Item "unlock_hash" | |
222 | .PD | |
223 | .Vb 1 | |
224 | \& lock_hash(%hash); | |
225 | .Ve | |
226 | .Sp | |
227 | \&\fIlock_hash()\fR locks an entire hash, making all keys and values readonly. | |
228 | No value can be changed, no keys can be added or deleted. | |
229 | .Sp | |
230 | .Vb 1 | |
231 | \& unlock_hash(%hash); | |
232 | .Ve | |
233 | .Sp | |
234 | \&\fIunlock_hash()\fR does the opposite of \fIlock_hash()\fR. All keys and values | |
235 | are made read/write. All values can be changed and keys can be added | |
236 | and deleted. | |
237 | .IP "\fBhash_seed\fR" 4 | |
238 | .IX Item "hash_seed" | |
239 | .Vb 1 | |
240 | \& my $hash_seed = hash_seed(); | |
241 | .Ve | |
242 | .Sp | |
243 | \&\fIhash_seed()\fR returns the seed number used to randomise hash ordering. | |
244 | Zero means the \*(L"traditional\*(R" random hash ordering, non-zero means the | |
245 | new even more random hash ordering introduced in Perl 5.8.1. | |
246 | .Sp | |
247 | \&\fBNote that the hash seed is sensitive information\fR: by knowing it one | |
248 | can craft a denial-of-service attack against Perl code, even remotely, | |
249 | see \*(L"Algorithmic Complexity Attacks\*(R" in perlsec for more information. | |
250 | \&\fBDo not disclose the hash seed\fR to people who don't need to know it. | |
251 | See also \*(L"\s-1PERL_HASH_SEED_DEBUG\s0\*(R" in perlrun. | |
252 | .SH "CAVEATS" | |
253 | .IX Header "CAVEATS" | |
254 | Note that the trapping of the restricted operations is not atomic: | |
255 | for example | |
256 | .PP | |
257 | .Vb 1 | |
258 | \& eval { %hash = (illegal_key => 1) } | |
259 | .Ve | |
260 | .PP | |
261 | leaves the \f(CW%hash\fR empty rather than with its original contents. | |
262 | .SH "AUTHOR" | |
263 | .IX Header "AUTHOR" | |
264 | Michael G Schwern <schwern@pobox.com> on top of code by Nick | |
265 | Ing-Simmons and Jeffrey Friedl. | |
266 | .SH "SEE ALSO" | |
267 | .IX Header "SEE ALSO" | |
268 | Scalar::Util, List::Util, Hash::Util, | |
269 | and \*(L"Algorithmic Complexity Attacks\*(R" in perlsec. |