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1 | =head1 NAME |
2 | |
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3 | perldelta - what's new for perl5.004 |
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4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | This document describes differences between the 5.003 release (as |
8 | documented in I<Programming Perl>, second edition--the Camel Book) and |
9 | this one. |
10 | |
11 | =head1 Supported Environments |
12 | |
13 | Perl5.004 builds out of the box on Unix, Plan9, LynxOS, VMS, OS/2, |
14 | QNX, and AmigaOS. |
15 | |
16 | =head1 Core Changes |
17 | |
18 | Most importantly, many bugs were fixed. See the F<Changes> |
19 | file in the distribution for details. |
20 | |
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21 | =head2 Compilation option: Binary compatibility with 5.003 |
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22 | |
23 | There is a new Configure question that asks if you want to maintain |
24 | binary compatibility with Perl 5.003. If you choose binary |
25 | compatibility, you do not have to recompile your extensions, but you |
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26 | might have symbol conflicts if you embed Perl in another application, |
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27 | just as in the 5.003 release. By default, binary compatibility |
28 | is preserved at the expense of symbol table pollution. |
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29 | |
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30 | =head2 $PERL5OPT environment variable |
31 | |
32 | You may now put Perl options in the $PERL5OPT environment variable. |
33 | Unless Perl is running with taint checks, it will interpret this |
34 | variable as if its contents had appeared on a "#!perl" line at the |
35 | beginning of your script, except that hyphens are optional. PERL5OPT |
36 | may only be used to set the following switches: B<-[DIMUdmw]>. |
37 | |
38 | =head2 More precise warnings |
39 | |
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40 | If you removed the B<-w> option from your Perl 5.003 scripts because it |
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41 | made Perl too verbose, we recommend that you try putting it back when |
42 | you upgrade to Perl 5.004. Each new perl version tends to remove some |
43 | undesirable warnings, while adding new warnings that may catch bugs in |
44 | your scripts. |
45 | |
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46 | =head2 Deprecated: Inherited C<AUTOLOAD> for non-methods |
47 | |
48 | Before Perl 5.004, C<AUTOLOAD> functions were looked up as methods |
49 | (using the C<@ISA> hierarchy), even when the function to be autoloaded |
50 | was called as a plain function (e.g. C<Foo::bar()>), not a method |
51 | (e.g. C<Foo->bar()> or C<$obj->bar()>). |
52 | |
53 | Perl 5.005 will use method lookup only for methods' C<AUTOLOAD>s. |
54 | However, there is a significant base of existing code that may be using |
55 | the old behavior. So, as an interim step, Perl 5.004 issues an optional |
56 | warning when a non-method uses an inherited C<AUTOLOAD>. |
57 | |
58 | The simple rule is: Inheritance will not work when autoloading |
59 | non-methods. The simple fix for old code is: In any module that used to |
60 | depend on inheriting C<AUTOLOAD> for non-methods from a base class named |
61 | C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during startup. |
62 | |
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63 | =head2 Subroutine arguments created only when they're modified |
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64 | |
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65 | In Perl 5.004, nonexistent array and hash elements used as subroutine |
66 | parameters are brought into existence only if they are actually |
67 | assigned to (via C<@_>). |
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68 | |
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69 | Earlier versions of Perl vary in their handling of such arguments. |
70 | Perl versions 5.002 and 5.003 always brought them into existence. |
71 | Perl versions 5.000, 5.001, and 5.002 brought them into existence only |
72 | if they were not the first argument (which was almost certainly a |
73 | bug). Earlier versions of Perl never brought them into existence. |
74 | |
75 | For example, given this code: |
76 | |
77 | undef @a; undef %a; |
78 | sub show { print $_[0] }; |
79 | sub change { $_[0]++ }; |
80 | show($a[2]); |
81 | change($a{b}); |
82 | |
83 | After this code executes in Perl 5.004, $a{b} exists but $a[2] does |
84 | not. In Perl 5.002 and 5.003, both $a{b} and $a[2] would have existed |
85 | (but $a[2]'s value would have been undefined). |
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86 | |
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87 | =head2 C<$)> is writable |
88 | |
89 | The C<$)> special variable has always (well, in Perl 5, at least) |
90 | reflected not only the current effective group, but also the group |
91 | list as returned by the C<getgroups()> C function (if there is one). |
92 | However, due to an oversight, assigning to C<$)> has not called |
93 | C<setgroups()>, only C<setegid()>. |
94 | |
95 | In Perl 5.004, assigning to C<$)> is exactly symmetrical with |
96 | examining it: The first number in its string value is used as the |
97 | effective gid, and all the others are passed to the C<setgroups()> C |
98 | function (if there is one). |
99 | |
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100 | =head2 Fixed parsing of $$<digit>, &$<digit>, etc. |
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101 | |
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102 | Perl versions before 5.004 misinterpreted any type marker followed by |
103 | "$" and a digit. For example, "$$0" was incorrectly taken to mean |
104 | "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004. |
105 | |
106 | However, the developers of Perl 5.004 could not fix this bug completely, |
107 | because at least two widely-used modules depend on the old meaning of |
108 | "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the |
109 | old (broken) way inside strings; but it generates this message as a |
110 | warning. And in Perl 5.005, this special treatment will cease. |
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111 | |
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112 | =head2 No resetting of $. on implicit close |
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113 | |
114 | The documentation for Perl 5.0 has always stated that C<$.> is I<not> |
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115 | reset when an already-open file handle is reopened with no intervening |
116 | call to C<close>. Due to a bug, perl versions 5.000 through 5.003 |
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117 | I<did> reset C<$.> under that circumstance; Perl 5.004 does not. |
118 | |
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119 | =head2 C<wantarray> may return undef |
120 | |
121 | The C<wantarray> operator returns true if a subroutine is expected to |
122 | return a list, and false otherwise. In Perl 5.004, C<wantarray> can |
123 | also return the undefined value if a subroutine's return value will |
124 | not be used at all, which allows subroutines to avoid a time-consuming |
125 | calculation of a return value if it isn't going to be used. |
126 | |
127 | =head2 Changes to tainting checks |
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128 | |
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129 | A bug in previous versions may have failed to detect some insecure |
130 | conditions when taint checks are turned on. (Taint checks are used |
131 | in setuid or setgid scripts, or when explicitly turned on with the |
132 | C<-T> invocation option.) Although it's unlikely, this may cause a |
133 | previously-working script to now fail -- which should be construed |
134 | as a blessing, since that indicates a potentially-serious security |
135 | hole was just plugged. |
136 | |
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137 | =head2 New Opcode module and revised Safe module |
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138 | |
139 | A new Opcode module supports the creation, manipulation and |
140 | application of opcode masks. The revised Safe module has a new API |
141 | and is implemented using the new Opcode module. Please read the new |
142 | Opcode and Safe documentation. |
143 | |
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144 | =head2 Embedding improvements |
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145 | |
146 | In older versions of Perl it was not possible to create more than one |
147 | Perl interpreter instance inside a single process without leaking like a |
148 | sieve and/or crashing. The bugs that caused this behavior have all been |
149 | fixed. However, you still must take care when embedding Perl in a C |
150 | program. See the updated perlembed manpage for tips on how to manage |
151 | your interpreters. |
152 | |
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153 | =head2 Internal change: FileHandle class based on IO::* classes |
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154 | |
155 | File handles are now stored internally as type IO::Handle. The |
156 | FileHandle module is still supported for backwards compatibility, but |
157 | it is now merely a front end to the IO::* modules -- specifically, |
158 | IO::Handle, IO::Seekable, and IO::File. We suggest, but do not |
159 | require, that you use the IO::* modules in new code. |
160 | |
161 | In harmony with this change, C<*GLOB{FILEHANDLE}> is now a |
162 | backward-compatible synonym for C<*STDOUT{IO}>. |
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163 | |
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164 | =head2 Internal change: PerlIO abstraction interface |
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165 | |
166 | It is now possible to build Perl with AT&T's sfio IO package |
167 | instead of stdio. See L<perlapio> for more details, and |
168 | the F<INSTALL> file for how to use it. |
169 | |
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170 | =head2 New and changed builtin variables |
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171 | |
172 | =over |
173 | |
174 | =item $^E |
175 | |
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176 | Extended error message on some platforms. (Also known as |
177 | $EXTENDED_OS_ERROR if you C<use English>). |
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178 | |
179 | =item $^H |
180 | |
181 | The current set of syntax checks enabled by C<use strict>. See the |
182 | documentation of C<strict> for more details. Not actually new, but |
183 | newly documented. |
184 | Because it is intended for internal use by Perl core components, |
185 | there is no C<use English> long name for this variable. |
186 | |
187 | =item $^M |
188 | |
189 | By default, running out of memory it is not trappable. However, if |
190 | compiled for this, Perl may use the contents of C<$^M> as an emergency |
191 | pool after die()ing with this message. Suppose that your Perl were |
192 | compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then |
193 | |
194 | $^M = 'a' x (1<<16); |
195 | |
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196 | would allocate a 64K buffer for use when in emergency. |
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197 | See the F<INSTALL> file for information on how to enable this option. |
198 | As a disincentive to casual use of this advanced feature, |
199 | there is no C<use English> long name for this variable. |
200 | |
201 | =back |
202 | |
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203 | =head2 New and changed builtin functions |
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204 | |
205 | =over |
206 | |
207 | =item delete on slices |
208 | |
209 | This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>) |
210 | |
211 | =item flock |
212 | |
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213 | is now supported on more platforms, prefers fcntl to lockf when |
214 | emulating, and always flushes before (un)locking. |
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215 | |
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216 | =item printf and sprintf |
217 | |
218 | now support "%i" as a synonym for "%d", and the "h" modifier. |
219 | So "%hi" means "short integer in decimal", and "%ho" means |
220 | "unsigned short integer as octal". |
221 | |
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222 | =item keys as an lvalue |
223 | |
224 | As an lvalue, C<keys> allows you to increase the number of hash buckets |
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225 | allocated for the given hash. This can gain you a measure of efficiency if |
226 | you know the hash is going to get big. (This is similar to pre-extending |
227 | an array by assigning a larger number to $#array.) If you say |
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228 | |
229 | keys %hash = 200; |
230 | |
231 | then C<%hash> will have at least 200 buckets allocated for it. These |
232 | buckets will be retained even if you do C<%hash = ()>; use C<undef |
233 | %hash> if you want to free the storage while C<%hash> is still in scope. |
234 | You can't shrink the number of buckets allocated for the hash using |
235 | C<keys> in this way (but you needn't worry about doing this by accident, |
236 | as trying has no effect). |
237 | |
238 | =item my() in Control Structures |
239 | |
240 | You can now use my() (with or without the parentheses) in the control |
241 | expressions of control structures such as: |
242 | |
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243 | while (defined(my $line = <>)) { |
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244 | $line = lc $line; |
245 | } continue { |
246 | print $line; |
247 | } |
248 | |
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249 | if ((my $answer = <STDIN>) =~ /^y(es)?$/i) { |
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250 | user_agrees(); |
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251 | } elsif ($answer =~ /^n(o)?$/i) { |
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252 | user_disagrees(); |
253 | } else { |
254 | chomp $answer; |
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255 | die "`$answer' is neither `yes' nor `no'"; |
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256 | } |
257 | |
258 | Also, you can declare a foreach loop control variable as lexical by |
259 | preceding it with the word "my". For example, in: |
260 | |
261 | foreach my $i (1, 2, 3) { |
262 | some_function(); |
263 | } |
264 | |
265 | $i is a lexical variable, and the scope of $i extends to the end of |
266 | the loop, but not beyond it. |
267 | |
268 | Note that you still cannot use my() on global punctuation variables |
269 | such as $_ and the like. |
270 | |
271 | =item unpack() and pack() |
272 | |
273 | A new format 'w' represents a BER compressed integer (as defined in |
274 | ASN.1). Its format is a sequence of one or more bytes, each of which |
275 | provides seven bits of the total value, with the most significant |
276 | first. Bit eight of each byte is set, except for the last byte, in |
277 | which bit eight is clear. |
278 | |
279 | =item use VERSION |
280 | |
281 | If the first argument to C<use> is a number, it is treated as a version |
282 | number instead of a module name. If the version of the Perl interpreter |
283 | is less than VERSION, then an error message is printed and Perl exits |
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284 | immediately. Because C<use> occurs at compile time, this check happens |
285 | immediately during the compilation process, unlike C<require VERSION>, |
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286 | which waits until runtime for the check. This is often useful if you |
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287 | need to check the current Perl version before C<use>ing library modules |
288 | which have changed in incompatible ways from older versions of Perl. |
289 | (We try not to do this more than we have to.) |
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290 | |
291 | =item use Module VERSION LIST |
292 | |
293 | If the VERSION argument is present between Module and LIST, then the |
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294 | C<use> will call the VERSION method in class Module with the given |
295 | version as an argument. The default VERSION method, inherited from |
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296 | the UNIVERSAL class, croaks if the given version is larger than the |
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297 | value of the variable $Module::VERSION. (Note that there is not a |
298 | comma after VERSION!) |
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299 | |
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300 | This version-checking mechanism is similar to the one currently used |
301 | in the Exporter module, but it is faster and can be used with modules |
302 | that don't use the Exporter. It is the recommended method for new |
303 | code. |
304 | |
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305 | =item prototype(FUNCTION) |
306 | |
307 | Returns the prototype of a function as a string (or C<undef> if the |
308 | function has no prototype). FUNCTION is a reference to or the name of the |
309 | function whose prototype you want to retrieve. |
310 | (Not actually new; just never documented before.) |
311 | |
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312 | =item srand |
313 | |
314 | The default seed for C<srand>, which used to be C<time>, has been changed. |
315 | Now it's a heady mix of difficult-to-predict system-dependent values, |
316 | which should be sufficient for most everyday purposes. |
317 | |
318 | Previous to version 5.004, calling C<rand> without first calling C<srand> |
319 | would yield the same sequence of random numbers on most or all machines. |
320 | Now, when perl sees that you're calling C<rand> and haven't yet called |
321 | C<srand>, it calls C<srand> with the default seed. You should still call |
322 | C<srand> manually if your code might ever be run on a pre-5.004 system, |
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323 | of course, or if you want a seed other than the default. |
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324 | |
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325 | =item $_ as Default |
326 | |
327 | Functions documented in the Camel to default to $_ now in |
328 | fact do, and all those that do are so documented in L<perlfunc>. |
329 | |
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330 | =item C<m//g> does not trigger a pos() reset on failure |
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331 | |
332 | The C<m//g> match iteration construct used to reset the iteration |
333 | when it failed to match (so that the next C<m//g> match would start at |
334 | the beginning of the string). You now have to explicitly do a |
335 | C<pos $str = 0;> to reset the "last match" position, or modify the |
336 | string in some way. This change makes it practical to chain C<m//g> |
337 | matches together in conjunction with ordinary matches using the C<\G> |
338 | zero-width assertion. See L<perlop> and L<perlre>. |
339 | |
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340 | =item C<m//x> ignores whitespace before ?*+{} |
341 | |
342 | The C<m//x> construct has always been intended to ignore all unescaped |
343 | whitespace. However, before Perl 5.004, whitespace had the effect of |
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344 | escaping repeat modifiers like "*" or "?"; for example, C</a *b/x> was |
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345 | (mis)interpreted as C</a\*b/x>. This bug has been fixed in 5.004. |
346 | |
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347 | =item nested C<sub{}> closures work now |
348 | |
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349 | Prior to the 5.004 release, nested anonymous functions didn't work |
350 | right. They do now. |
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351 | |
352 | =item formats work right on changing lexicals |
353 | |
354 | Just like anonymous functions that contain lexical variables |
355 | that change (like a lexical index variable for a C<foreach> loop), |
356 | formats now work properly. For example, this silently failed |
357 | before, and is fine now: |
358 | |
359 | my $i; |
360 | foreach $i ( 1 .. 10 ) { |
361 | format = |
362 | my i is @# |
363 | $i |
364 | . |
365 | write; |
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366 | } |
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367 | |
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368 | =back |
369 | |
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370 | =head2 New builtin methods |
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371 | |
372 | The C<UNIVERSAL> package automatically contains the following methods that |
373 | are inherited by all other classes: |
374 | |
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375 | =over |
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376 | |
377 | =item isa(CLASS) |
378 | |
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379 | C<isa> returns I<true> if its object is blessed into a subclass of C<CLASS> |
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380 | |
381 | C<isa> is also exportable and can be called as a sub with two arguments. This |
382 | allows the ability to check what a reference points to. Example: |
383 | |
384 | use UNIVERSAL qw(isa); |
385 | |
386 | if(isa($ref, 'ARRAY')) { |
387 | ... |
388 | } |
389 | |
390 | =item can(METHOD) |
391 | |
392 | C<can> checks to see if its object has a method called C<METHOD>, |
393 | if it does then a reference to the sub is returned; if it does not then |
394 | I<undef> is returned. |
395 | |
396 | =item VERSION( [NEED] ) |
397 | |
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398 | C<VERSION> returns the version number of the class (package). If the |
399 | NEED argument is given then it will check that the current version (as |
400 | defined by the $VERSION variable in the given package) not less than |
401 | NEED; it will die if this is not the case. This method is normally |
402 | called as a class method. This method is called automatically by the |
403 | C<VERSION> form of C<use>. |
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404 | |
405 | use A 1.2 qw(some imported subs); |
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406 | # implies: |
407 | A->VERSION(1.2); |
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408 | |
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409 | =back |
410 | |
411 | B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and |
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412 | C<isa> uses a very similar method and caching strategy. This may cause |
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413 | strange effects if the Perl code dynamically changes @ISA in any package. |
414 | |
415 | You may add other methods to the UNIVERSAL class via Perl or XS code. |
416 | You do not need to C<use UNIVERSAL> in order to make these methods |
417 | available to your program. This is necessary only if you wish to |
418 | have C<isa> available as a plain subroutine in the current package. |
419 | |
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420 | =head2 TIEHANDLE now supported |
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421 | |
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422 | See L<perltie> for other kinds of tie()s. |
423 | |
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424 | =over |
425 | |
426 | =item TIEHANDLE classname, LIST |
427 | |
428 | This is the constructor for the class. That means it is expected to |
429 | return an object of some sort. The reference can be used to |
430 | hold some internal information. |
431 | |
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432 | sub TIEHANDLE { |
433 | print "<shout>\n"; |
434 | my $i; |
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435 | return bless \$i, shift; |
436 | } |
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437 | |
438 | =item PRINT this, LIST |
439 | |
440 | This method will be triggered every time the tied handle is printed to. |
441 | Beyond its self reference it also expects the list that was passed to |
442 | the print function. |
443 | |
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444 | sub PRINT { |
445 | $r = shift; |
446 | $$r++; |
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447 | return print join( $, => map {uc} @_), $\; |
448 | } |
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449 | |
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450 | =item READ this LIST |
451 | |
452 | This method will be called when the handle is read from via the C<read> |
453 | or C<sysread> functions. |
454 | |
455 | sub READ { |
456 | $r = shift; |
457 | my($buf,$len,$offset) = @_; |
458 | print "READ called, \$buf=$buf, \$len=$len, \$offset=$offset"; |
459 | } |
460 | |
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461 | =item READLINE this |
462 | |
463 | This method will be called when the handle is read from. The method |
464 | should return undef when there is no more data. |
465 | |
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466 | sub READLINE { |
467 | $r = shift; |
468 | return "PRINT called $$r times\n" |
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469 | } |
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470 | |
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471 | =item GETC this |
472 | |
473 | This method will be called when the C<getc> function is called. |
474 | |
475 | sub GETC { print "Don't GETC, Get Perl"; return "a"; } |
476 | |
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477 | =item DESTROY this |
478 | |
479 | As with the other types of ties, this method will be called when the |
480 | tied handle is about to be destroyed. This is useful for debugging and |
481 | possibly for cleaning up. |
482 | |
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483 | sub DESTROY { |
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484 | print "</shout>\n"; |
485 | } |
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486 | |
487 | =back |
488 | |
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489 | =head2 Malloc enhancements |
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490 | |
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491 | Four new compilation flags are recognized by malloc.c. (They have no |
492 | effect if perl is compiled with system malloc().) |
493 | |
494 | =over |
495 | |
496 | =item -DDEBUGGING_MSTATS |
497 | |
498 | If perl is compiled with C<DEBUGGING_MSTATS> defined, you can print |
499 | memory statistics at runtime by running Perl thusly: |
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500 | |
501 | env PERL_DEBUG_MSTATS=2 perl your_script_here |
502 | |
503 | The value of 2 means to print statistics after compilation and on |
504 | exit; with a value of 1, the statistics ares printed only on exit. |
505 | (If you want the statistics at an arbitrary time, you'll need to |
506 | install the optional module Devel::Peek.) |
507 | |
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508 | =item -DEMERGENCY_SBRK |
509 | |
510 | If this macro is defined, running out of memory need not be a fatal |
511 | error: a memory pool can allocated by assigning to the special |
512 | variable C<$^M>. See L<"$^M">. |
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513 | |
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514 | =item -DPACK_MALLOC |
515 | |
516 | Perl memory allocation is by bucket with sizes close to powers of two. |
517 | Because of these malloc overhead may be big, especially for data of |
518 | size exactly a power of two. If C<PACK_MALLOC> is defined, perl uses |
519 | a slightly different algorithm for small allocations (up to 64 bytes |
520 | long), which makes it possible to have overhead down to 1 byte for |
521 | allocations which are powers of two (and appear quite often). |
522 | |
523 | Expected memory savings (with 8-byte alignment in C<alignbytes>) is |
524 | about 20% for typical Perl usage. Expected slowdown due to additional |
525 | malloc overhead is in fractions of a percent (hard to measure, because |
526 | of the effect of saved memory on speed). |
527 | |
528 | =item -DTWO_POT_OPTIMIZE |
529 | |
530 | Similarly to C<PACK_MALLOC>, this macro improves allocations of data |
531 | with size close to a power of two; but this works for big allocations |
532 | (starting with 16K by default). Such allocations are typical for big |
533 | hashes and special-purpose scripts, especially image processing. |
534 | |
535 | On recent systems, the fact that perl requires 2M from system for 1M |
536 | allocation will not affect speed of execution, since the tail of such |
537 | a chunk is not going to be touched (and thus will not require real |
538 | memory). However, it may result in a premature out-of-memory error. |
539 | So if you will be manipulating very large blocks with sizes close to |
540 | powers of two, it would be wise to define this macro. |
541 | |
542 | Expected saving of memory is 0-100% (100% in applications which |
543 | require most memory in such 2**n chunks); expected slowdown is |
544 | negligible. |
545 | |
546 | =back |
547 | |
54310121 |
548 | =head2 Miscellaneous efficiency enhancements |
774d564b |
549 | |
550 | Functions that have an empty prototype and that do nothing but return |
551 | a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>). |
552 | |
aa689395 |
553 | Each unique hash key is only allocated once, no matter how many hashes |
554 | have an entry with that key. So even if you have 100 copies of the |
68dc0745 |
555 | same hash, the hash keys never have to be reallocated. |
aa689395 |
556 | |
5f05dabc |
557 | =head1 Pragmata |
558 | |
54310121 |
559 | Six new pragmatic modules exist: |
5f05dabc |
560 | |
561 | =over |
562 | |
54310121 |
563 | =item use autouse MODULE => qw(sub1 sub2 sub3) |
564 | |
565 | Defers C<require MODULE> until someone calls one of the specified |
566 | subroutines (which must be exported by MODULE). This pragma should be |
567 | used with caution, and only when necessary. |
568 | |
5f05dabc |
569 | =item use blib |
570 | |
774d564b |
571 | =item use blib 'dir' |
572 | |
5f05dabc |
573 | Looks for MakeMaker-like I<'blib'> directory structure starting in |
574 | I<dir> (or current directory) and working back up to five levels of |
575 | parent directories. |
576 | |
577 | Intended for use on command line with B<-M> option as a way of testing |
578 | arbitrary scripts against an uninstalled version of a package. |
579 | |
54310121 |
580 | =item use constant NAME => VALUE |
581 | |
582 | Provides a convenient interface for creating compile-time constants, |
583 | See L<perlsub/"Constant Functions">. |
584 | |
5f05dabc |
585 | =item use locale |
586 | |
587 | Tells the compiler to enable (or disable) the use of POSIX locales for |
54310121 |
588 | builtin operations. |
5f05dabc |
589 | |
590 | When C<use locale> is in effect, the current LC_CTYPE locale is used |
591 | for regular expressions and case mapping; LC_COLLATE for string |
592 | ordering; and LC_NUMERIC for numeric formating in printf and sprintf |
593 | (but B<not> in print). LC_NUMERIC is always used in write, since |
594 | lexical scoping of formats is problematic at best. |
595 | |
596 | Each C<use locale> or C<no locale> affects statements to the end of |
597 | the enclosing BLOCK or, if not inside a BLOCK, to the end of the |
598 | current file. Locales can be switched and queried with |
599 | POSIX::setlocale(). |
600 | |
601 | See L<perllocale> for more information. |
602 | |
603 | =item use ops |
604 | |
7cfe7857 |
605 | Disable unsafe opcodes, or any named opcodes, when compiling Perl code. |
5f05dabc |
606 | |
ff0cee69 |
607 | =item use vmsish |
608 | |
609 | Enable VMS-specific language features. Currently, there are three |
aa689395 |
610 | VMS-specific features available: 'status', which makes C<$?> and |
ff0cee69 |
611 | C<system> return genuine VMS status values instead of emulating POSIX; |
612 | 'exit', which makes C<exit> take a genuine VMS status value instead of |
613 | assuming that C<exit 1> is an error; and 'time', which makes all times |
614 | relative to the local time zone, in the VMS tradition. |
615 | |
5f05dabc |
616 | =back |
617 | |
618 | =head1 Modules |
619 | |
5cd24f17 |
620 | =head2 Required Updates |
621 | |
622 | Though Perl 5.004 is compatible with almost all modules that work |
623 | with Perl 5.003, there are a few exceptions: |
624 | |
625 | Module Required Version for Perl 5.004 |
626 | ------ ------------------------------- |
627 | Filter 1.12 |
628 | LWP 5.08 |
629 | Tk Tk400.202 (-w makes noise) |
630 | |
54310121 |
631 | =head2 Installation directories |
f86702cc |
632 | |
633 | The I<installperl> script now places the Perl source files for |
634 | extensions in the architecture-specific library directory, which is |
635 | where the shared libraries for extensions have always been. This |
636 | change is intended to allow administrators to keep the Perl 5.004 |
637 | library directory unchanged from a previous version, without running |
638 | the risk of binary incompatibility between extensions' Perl source and |
639 | shared libraries. |
640 | |
54310121 |
641 | =head2 Module information summary |
5f05dabc |
642 | |
774d564b |
643 | Brand new modules, arranged by topic rather than strictly |
644 | alphabetically: |
645 | |
646 | CPAN interface to Comprehensive Perl Archive Network |
647 | CPAN::FirstTime create a CPAN configuration file |
648 | CPAN::Nox run CPAN while avoiding compiled extensions |
5f05dabc |
649 | |
650 | IO.pm Top-level interface to IO::* classes |
651 | IO/File.pm IO::File extension Perl module |
652 | IO/Handle.pm IO::Handle extension Perl module |
653 | IO/Pipe.pm IO::Pipe extension Perl module |
654 | IO/Seekable.pm IO::Seekable extension Perl module |
655 | IO/Select.pm IO::Select extension Perl module |
656 | IO/Socket.pm IO::Socket extension Perl module |
657 | |
658 | Opcode.pm Disable named opcodes when compiling Perl code |
659 | |
660 | ExtUtils/Embed.pm Utilities for embedding Perl in C programs |
661 | ExtUtils/testlib.pm Fixes up @INC to use just-built extension |
662 | |
5f05dabc |
663 | FindBin.pm Find path of currently executing program |
664 | |
665 | Class/Template.pm Structure/member template builder |
666 | File/stat.pm Object-oriented wrapper around CORE::stat |
667 | Net/hostent.pm Object-oriented wrapper around CORE::gethost* |
668 | Net/netent.pm Object-oriented wrapper around CORE::getnet* |
669 | Net/protoent.pm Object-oriented wrapper around CORE::getproto* |
670 | Net/servent.pm Object-oriented wrapper around CORE::getserv* |
671 | Time/gmtime.pm Object-oriented wrapper around CORE::gmtime |
672 | Time/localtime.pm Object-oriented wrapper around CORE::localtime |
673 | Time/tm.pm Perl implementation of "struct tm" for {gm,local}time |
674 | User/grent.pm Object-oriented wrapper around CORE::getgr* |
675 | User/pwent.pm Object-oriented wrapper around CORE::getpw* |
676 | |
774d564b |
677 | Tie/RefHash.pm Base class for tied hashes with references as keys |
7a4c00b4 |
678 | |
5f05dabc |
679 | UNIVERSAL.pm Base class for *ALL* classes |
680 | |
54310121 |
681 | =head2 Fcntl |
682 | |
683 | New constants in the existing Fcntl modules are now supported, |
684 | provided that your operating system happens to support them: |
685 | |
686 | F_GETOWN F_SETOWN |
687 | O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC |
688 | O_EXLOCK O_SHLOCK |
689 | |
690 | These constants are intended for use with the Perl operators sysopen() |
691 | and fcntl() and the basic database modules like SDBM_File. For the |
692 | exact meaning of these and other Fcntl constants please refer to your |
693 | operating system's documentation for fcntl() and open(). |
694 | |
695 | In addition, the Fcntl module now provides these constants for use |
696 | with the Perl operator flock(): |
697 | |
698 | LOCK_SH LOCK_EX LOCK_NB LOCK_UN |
699 | |
700 | These constants are defined in all environments (because where there is |
701 | no flock() system call, Perl emulates it). However, for historical |
702 | reasons, these constants are not exported unless they are explicitly |
703 | requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>). |
704 | |
5f05dabc |
705 | =head2 IO |
706 | |
707 | The IO module provides a simple mechanism to load all of the IO modules at one |
708 | go. Currently this includes: |
709 | |
710 | IO::Handle |
711 | IO::Seekable |
712 | IO::File |
713 | IO::Pipe |
714 | IO::Socket |
715 | |
716 | For more information on any of these modules, please see its |
717 | respective documentation. |
718 | |
719 | =head2 Math::Complex |
720 | |
721 | The Math::Complex module has been totally rewritten, and now supports |
722 | more operations. These are overloaded: |
723 | |
724 | + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify) |
725 | |
726 | And these functions are now exported: |
727 | |
728 | pi i Re Im arg |
5cd24f17 |
729 | log10 logn ln cbrt root |
730 | tan |
731 | csc sec cot |
732 | asin acos atan |
733 | acsc asec acot |
734 | sinh cosh tanh |
735 | csch sech coth |
736 | asinh acosh atanh |
737 | acsch asech acoth |
5f05dabc |
738 | cplx cplxe |
739 | |
5aabfad6 |
740 | =head2 Math::Trig |
741 | |
5cd24f17 |
742 | This new module provides a simpler interface to parts of Math::Complex for |
5aabfad6 |
743 | those who need trigonometric functions only for real numbers. |
744 | |
0a753a76 |
745 | =head2 DB_File |
746 | |
747 | There have been quite a few changes made to DB_File. Here are a few of |
748 | the highlights: |
749 | |
750 | =over |
751 | |
752 | =item * |
753 | |
754 | Fixed a handful of bugs. |
755 | |
756 | =item * |
757 | |
758 | By public demand, added support for the standard hash function exists(). |
759 | |
760 | =item * |
761 | |
762 | Made it compatible with Berkeley DB 1.86. |
763 | |
764 | =item * |
765 | |
766 | Made negative subscripts work with RECNO interface. |
767 | |
768 | =item * |
769 | |
770 | Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default |
771 | mode from 0640 to 0666. |
772 | |
773 | =item * |
774 | |
775 | Made DB_File automatically import the open() constants (O_RDWR, |
776 | O_CREAT etc.) from Fcntl, if available. |
777 | |
778 | =item * |
779 | |
780 | Updated documentation. |
781 | |
782 | =back |
783 | |
784 | Refer to the HISTORY section in DB_File.pm for a complete list of |
785 | changes. Everything after DB_File 1.01 has been added since 5.003. |
786 | |
787 | =head2 Net::Ping |
788 | |
789 | Major rewrite - support added for both udp echo and real icmp pings. |
790 | |
54310121 |
791 | =head2 Object-oriented overrides for builtin operators |
5f05dabc |
792 | |
54310121 |
793 | Many of the Perl builtins returning lists now have |
5f05dabc |
794 | object-oriented overrides. These are: |
795 | |
796 | File::stat |
797 | Net::hostent |
798 | Net::netent |
799 | Net::protoent |
800 | Net::servent |
801 | Time::gmtime |
802 | Time::localtime |
803 | User::grent |
804 | User::pwent |
805 | |
806 | For example, you can now say |
807 | |
808 | use File::stat; |
809 | use User::pwent; |
810 | $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid); |
811 | |
774d564b |
812 | =head1 Utility Changes |
5f05dabc |
813 | |
774d564b |
814 | =head2 xsubpp |
5f05dabc |
815 | |
0a753a76 |
816 | =over |
817 | |
774d564b |
818 | =item C<void> XSUBs now default to returning nothing |
819 | |
820 | Due to a documentation/implementation bug in previous versions of |
821 | Perl, XSUBs with a return type of C<void> have actually been |
822 | returning one value. Usually that value was the GV for the XSUB, |
823 | but sometimes it was some already freed or reused value, which would |
824 | sometimes lead to program failure. |
825 | |
826 | In Perl 5.004, if an XSUB is declared as returning C<void>, it |
827 | actually returns no value, i.e. an empty list (though there is a |
828 | backward-compatibility exception; see below). If your XSUB really |
829 | does return an SV, you should give it a return type of C<SV *>. |
830 | |
831 | For backward compatibility, I<xsubpp> tries to guess whether a |
832 | C<void> XSUB is really C<void> or if it wants to return an C<SV *>. |
833 | It does so by examining the text of the XSUB: if I<xsubpp> finds |
834 | what looks like an assignment to C<ST(0)>, it assumes that the |
835 | XSUB's return type is really C<SV *>. |
5f05dabc |
836 | |
0a753a76 |
837 | =back |
838 | |
839 | =head1 C Language API Changes |
840 | |
841 | =over |
842 | |
843 | =item C<gv_fetchmethod> and C<perl_call_sv> |
844 | |
845 | The C<gv_fetchmethod> function finds a method for an object, just like |
846 | in Perl 5.003. The GV it returns may be a method cache entry. |
847 | However, in Perl 5.004, method cache entries are not visible to users; |
848 | therefore, they can no longer be passed directly to C<perl_call_sv>. |
849 | Instead, you should use the C<GvCV> macro on the GV to extract its CV, |
850 | and pass the CV to C<perl_call_sv>. |
851 | |
852 | The most likely symptom of passing the result of C<gv_fetchmethod> to |
853 | C<perl_call_sv> is Perl's producing an "Undefined subroutine called" |
854 | error on the I<second> call to a given method (since there is no cache |
855 | on the first call). |
856 | |
1e422769 |
857 | =item Extended API for manipulating hashes |
858 | |
859 | Internal handling of hash keys has changed. The old hashtable API is |
860 | still fully supported, and will likely remain so. The additions to the |
861 | API allow passing keys as C<SV*>s, so that C<tied> hashes can be given |
54310121 |
862 | real scalars as keys rather than plain strings (nontied hashes still |
1e422769 |
863 | can only use strings as keys). New extensions must use the new hash |
864 | access functions and macros if they wish to use C<SV*> keys. These |
865 | additions also make it feasible to manipulate C<HE*>s (hash entries), |
866 | which can be more efficient. See L<perlguts> for details. |
867 | |
0a753a76 |
868 | =back |
869 | |
5f05dabc |
870 | =head1 Documentation Changes |
871 | |
872 | Many of the base and library pods were updated. These |
873 | new pods are included in section 1: |
874 | |
0a753a76 |
875 | =over |
5f05dabc |
876 | |
774d564b |
877 | =item L<perldelta> |
5f05dabc |
878 | |
71be2cbc |
879 | This document. |
5f05dabc |
880 | |
71be2cbc |
881 | =item L<perllocale> |
5f05dabc |
882 | |
71be2cbc |
883 | Locale support (internationalization and localization). |
5f05dabc |
884 | |
885 | =item L<perltoot> |
886 | |
887 | Tutorial on Perl OO programming. |
888 | |
71be2cbc |
889 | =item L<perlapio> |
890 | |
891 | Perl internal IO abstraction interface. |
892 | |
5f05dabc |
893 | =item L<perldebug> |
894 | |
895 | Although not new, this has been massively updated. |
896 | |
897 | =item L<perlsec> |
898 | |
899 | Although not new, this has been massively updated. |
900 | |
901 | =back |
902 | |
903 | =head1 New Diagnostics |
904 | |
905 | Several new conditions will trigger warnings that were |
906 | silent before. Some only affect certain platforms. |
2ae324a7 |
907 | The following new warnings and errors outline these. |
774d564b |
908 | These messages are classified as follows (listed in |
909 | increasing order of desperation): |
910 | |
911 | (W) A warning (optional). |
912 | (D) A deprecation (optional). |
913 | (S) A severe warning (mandatory). |
914 | (F) A fatal error (trappable). |
915 | (P) An internal error you should never see (trappable). |
54310121 |
916 | (X) A very fatal error (nontrappable). |
774d564b |
917 | (A) An alien error message (not generated by Perl). |
5f05dabc |
918 | |
0a753a76 |
919 | =over |
5f05dabc |
920 | |
921 | =item "my" variable %s masks earlier declaration in same scope |
922 | |
923 | (S) A lexical variable has been redeclared in the same scope, effectively |
924 | eliminating all access to the previous instance. This is almost always |
925 | a typographical error. Note that the earlier variable will still exist |
926 | until the end of the scope or until all closure referents to it are |
927 | destroyed. |
928 | |
774d564b |
929 | =item %s argument is not a HASH element or slice |
930 | |
931 | (F) The argument to delete() must be either a hash element, such as |
932 | |
933 | $foo{$bar} |
934 | $ref->[12]->{"susie"} |
935 | |
936 | or a hash slice, such as |
937 | |
938 | @foo{$bar, $baz, $xyzzy} |
939 | @{$ref->[12]}{"susie", "queue"} |
940 | |
5f05dabc |
941 | =item Allocation too large: %lx |
942 | |
54310121 |
943 | (X) You can't allocate more than 64K on an MS-DOS machine. |
5f05dabc |
944 | |
945 | =item Allocation too large |
946 | |
947 | (F) You can't allocate more than 2^31+"small amount" bytes. |
948 | |
54310121 |
949 | =item Applying %s to %s will act on scalar(%s) |
950 | |
951 | (W) The pattern match (//), substitution (s///), and translation (tr///) |
952 | operators work on scalar values. If you apply one of them to an array |
953 | or a hash, it will convert the array or hash to a scalar value -- the |
954 | length of an array, or the population info of a hash -- and then work on |
955 | that scalar value. This is probably not what you meant to do. See |
956 | L<perlfunc/grep> and L<perlfunc/map> for alternatives. |
957 | |
958 | =item Attempt to free nonexistent shared string |
5f05dabc |
959 | |
960 | (P) Perl maintains a reference counted internal table of strings to |
961 | optimize the storage and access of hash keys and other strings. This |
962 | indicates someone tried to decrement the reference count of a string |
963 | that can no longer be found in the table. |
964 | |
965 | =item Attempt to use reference as lvalue in substr |
966 | |
967 | (W) You supplied a reference as the first argument to substr() used |
968 | as an lvalue, which is pretty strange. Perhaps you forgot to |
969 | dereference it first. See L<perlfunc/substr>. |
970 | |
774d564b |
971 | =item Can't use bareword ("%s") as %s ref while "strict refs" in use |
972 | |
973 | (F) Only hard references are allowed by "strict refs". Symbolic references |
974 | are disallowed. See L<perlref>. |
975 | |
54310121 |
976 | =item Cannot resolve method `%s' overloading `%s' in package `%s' |
977 | |
978 | (P) Internal error trying to resolve overloading specified by a method |
979 | name (as opposed to a subroutine reference). |
980 | |
774d564b |
981 | =item Constant subroutine %s redefined |
982 | |
983 | (S) You redefined a subroutine which had previously been eligible for |
dc848c6f |
984 | inlining. See L<perlsub/"Constant Functions"> for commentary and |
54310121 |
985 | workarounds. |
986 | |
987 | =item Constant subroutine %s undefined |
988 | |
989 | (S) You undefined a subroutine which had previously been eligible for |
774d564b |
990 | inlining. See L<perlsub/"Constant Functions"> for commentary and |
991 | workarounds. |
992 | |
54310121 |
993 | =item Copy method did not return a reference |
994 | |
995 | (F) The method which overloads "=" is buggy. See L<overload/Copy Constructor>. |
996 | |
774d564b |
997 | =item Died |
998 | |
999 | (F) You passed die() an empty string (the equivalent of C<die "">) or |
1000 | you called it with no args and both C<$@> and C<$_> were empty. |
1001 | |
54310121 |
1002 | =item Exiting pseudo-block via %s |
1003 | |
1004 | (W) You are exiting a rather special block construct (like a sort block or |
1005 | subroutine) by unconventional means, such as a goto, or a loop control |
1006 | statement. See L<perlfunc/sort>. |
1007 | |
1008 | =item Illegal character %s (carriage return) |
1009 | |
1010 | (F) A carriage return character was found in the input. This is an |
1011 | error, and not a warning, because carriage return characters can break |
1012 | multi-line strings, including here documents (e.g., C<print E<lt>E<lt>EOF;>). |
1013 | |
1014 | =item Illegal switch in PERL5OPT: %s |
1015 | |
1016 | (X) The PERL5OPT environment variable may only be used to set the |
1017 | following switches: B<-[DIMUdmw]>. |
1018 | |
5f05dabc |
1019 | =item Integer overflow in hex number |
1020 | |
1021 | (S) The literal hex number you have specified is too big for your |
1022 | architecture. On a 32-bit architecture the largest hex literal is |
1023 | 0xFFFFFFFF. |
1024 | |
1025 | =item Integer overflow in octal number |
1026 | |
1027 | (S) The literal octal number you have specified is too big for your |
1028 | architecture. On a 32-bit architecture the largest octal literal is |
1029 | 037777777777. |
1030 | |
5cd24f17 |
1031 | =item internal error: glob failed |
1032 | |
1033 | (P) Something went wrong with the external program(s) used for C<glob> |
1034 | and C<E<lt>*.cE<gt>>. This may mean that your csh (C shell) is |
1035 | broken. If so, you should change all of the csh-related variables in |
1036 | config.sh: If you have tcsh, make the variables refer to it as if it |
1037 | were csh (e.g. C<full_csh='/usr/bin/tcsh'>); otherwise, make them all |
1038 | empty (except that C<d_csh> should be C<'undef'>) so that Perl will |
1039 | think csh is missing. In either case, after editing config.sh, run |
1040 | C<./Configure -S> and rebuild Perl. |
1041 | |
774d564b |
1042 | =item Name "%s::%s" used only once: possible typo |
1043 | |
1044 | (W) Typographical errors often show up as unique variable names. |
1045 | If you had a good reason for having a unique name, then just mention |
1046 | it again somehow to suppress the message (the C<use vars> pragma is |
1047 | provided for just this purpose). |
1048 | |
5f05dabc |
1049 | =item Null picture in formline |
1050 | |
1051 | (F) The first argument to formline must be a valid format picture |
1052 | specification. It was found to be empty, which probably means you |
1053 | supplied it an uninitialized value. See L<perlform>. |
1054 | |
1055 | =item Offset outside string |
1056 | |
1057 | (F) You tried to do a read/write/send/recv operation with an offset |
1058 | pointing outside the buffer. This is difficult to imagine. |
1059 | The sole exception to this is that C<sysread()>ing past the buffer |
1060 | will extend the buffer and zero pad the new area. |
1061 | |
1062 | =item Out of memory! |
1063 | |
1064 | (X|F) The malloc() function returned 0, indicating there was insufficient |
1065 | remaining memory (or virtual memory) to satisfy the request. |
1066 | |
1067 | The request was judged to be small, so the possibility to trap it |
1068 | depends on the way Perl was compiled. By default it is not trappable. |
1069 | However, if compiled for this, Perl may use the contents of C<$^M> as |
1070 | an emergency pool after die()ing with this message. In this case the |
1071 | error is trappable I<once>. |
1072 | |
1073 | =item Out of memory during request for %s |
1074 | |
1075 | (F) The malloc() function returned 0, indicating there was insufficient |
1076 | remaining memory (or virtual memory) to satisfy the request. However, |
1077 | the request was judged large enough (compile-time default is 64K), so |
1078 | a possibility to shut down by trapping this error is granted. |
1079 | |
1080 | =item Possible attempt to put comments in qw() list |
1081 | |
774d564b |
1082 | (W) qw() lists contain items separated by whitespace; as with literal |
1083 | strings, comment characters are not ignored, but are instead treated |
1084 | as literal data. (You may have used different delimiters than the |
1085 | exclamation marks parentheses shown here; braces are also frequently |
1086 | used.) |
1087 | |
1088 | You probably wrote something like this: |
5f05dabc |
1089 | |
2ae324a7 |
1090 | @list = qw( |
774d564b |
1091 | a # a comment |
5f05dabc |
1092 | b # another comment |
774d564b |
1093 | ); |
5f05dabc |
1094 | |
1095 | when you should have written this: |
1096 | |
774d564b |
1097 | @list = qw( |
2ae324a7 |
1098 | a |
5f05dabc |
1099 | b |
774d564b |
1100 | ); |
1101 | |
1102 | If you really want comments, build your list the |
1103 | old-fashioned way, with quotes and commas: |
1104 | |
1105 | @list = ( |
1106 | 'a', # a comment |
1107 | 'b', # another comment |
1108 | ); |
5f05dabc |
1109 | |
1110 | =item Possible attempt to separate words with commas |
1111 | |
774d564b |
1112 | (W) qw() lists contain items separated by whitespace; therefore commas |
1113 | aren't needed to separate the items. (You may have used different |
1114 | delimiters than the parentheses shown here; braces are also frequently |
1115 | used.) |
5f05dabc |
1116 | |
2ae324a7 |
1117 | You probably wrote something like this: |
5f05dabc |
1118 | |
774d564b |
1119 | qw! a, b, c !; |
1120 | |
1121 | which puts literal commas into some of the list items. Write it without |
1122 | commas if you don't want them to appear in your data: |
1123 | |
1124 | qw! a b c !; |
5f05dabc |
1125 | |
5cd24f17 |
1126 | =item Recursive substitution detected |
1127 | |
1128 | (F) The replacement string of a substitution caused the recursive |
1129 | execution of that very same substituion. Perl cannot keep track of |
1130 | special variables (C<$1>, etc.) under such circumstances. |
1131 | |
774d564b |
1132 | =item Scalar value @%s{%s} better written as $%s{%s} |
1133 | |
1134 | (W) You've used a hash slice (indicated by @) to select a single element of |
1135 | a hash. Generally it's better to ask for a scalar value (indicated by $). |
1136 | The difference is that C<$foo{&bar}> always behaves like a scalar, both when |
1137 | assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves |
1138 | like a list when you assign to it, and provides a list context to its |
1139 | subscript, which can do weird things if you're expecting only one subscript. |
5f05dabc |
1140 | |
54310121 |
1141 | =item Stub found while resolving method `%s' overloading `%s' in package `%s' |
1142 | |
1143 | (P) Overloading resolution over @ISA tree may be broken by importing stubs. |
1144 | Stubs should never be implicitely created, but explicit calls to C<can> |
1145 | may break this. |
1146 | |
1147 | =item Too late for "B<-T>" option |
1148 | |
1149 | (X) The #! line (or local equivalent) in a Perl script contains the |
1150 | B<-T> option, but Perl was not invoked with B<-T> in its argument |
1151 | list. This is an error because, by the time Perl discovers a B<-T> in |
1152 | a script, it's too late to properly taint everything from the |
1153 | environment. So Perl gives up. |
1154 | |
5f05dabc |
1155 | =item untie attempted while %d inner references still exist |
1156 | |
1157 | (W) A copy of the object returned from C<tie> (or C<tied>) was still |
1158 | valid when C<untie> was called. |
1159 | |
54310121 |
1160 | =item Unrecognized character %s |
1161 | |
1162 | (F) The Perl parser has no idea what to do with the specified character |
1163 | in your Perl script (or eval). Perhaps you tried to run a compressed |
1164 | script, a binary program, or a directory as a Perl program. |
1165 | |
1166 | =item Unsupported function fork |
1167 | |
1168 | (F) Your version of executable does not support forking. |
1169 | |
1170 | Note that under some systems, like OS/2, there may be different flavors of |
1171 | Perl executables, some of which may support fork, some not. Try changing |
1172 | the name you call Perl by to C<perl_>, C<perl__>, and so on. |
1173 | |
5cd24f17 |
1174 | =item Use of "$$<digit>" to mean "${$}<digit>" is deprecated |
1175 | |
1176 | (D) Perl versions before 5.004 misinterpreted any type marker followed |
1177 | by "$" and a digit. For example, "$$0" was incorrectly taken to mean |
1178 | "${$}0" instead of "${$0}". This bug is (mostly) fixed in Perl 5.004. |
1179 | |
1180 | However, the developers of Perl 5.004 could not fix this bug completely, |
1181 | because at least two widely-used modules depend on the old meaning of |
1182 | "$$0" in a string. So Perl 5.004 still interprets "$$<digit>" in the |
1183 | old (broken) way inside strings; but it generates this message as a |
1184 | warning. And in Perl 5.005, this special treatment will cease. |
1185 | |
54310121 |
1186 | =item Value of %s can be "0"; test with defined() |
774d564b |
1187 | |
54310121 |
1188 | (W) In a conditional expression, you used <HANDLE>, <*> (glob), C<each()>, |
1189 | or C<readdir()> as a boolean value. Each of these constructs can return a |
1190 | value of "0"; that would make the conditional expression false, which is |
1191 | probably not what you intended. When using these constructs in conditional |
1192 | expressions, test their values with the C<defined> operator. |
774d564b |
1193 | |
1194 | =item Variable "%s" may be unavailable |
1195 | |
1196 | (W) An inner (nested) I<anonymous> subroutine is inside a I<named> |
1197 | subroutine, and outside that is another subroutine; and the anonymous |
1198 | (innermost) subroutine is referencing a lexical variable defined in |
1199 | the outermost subroutine. For example: |
1200 | |
1201 | sub outermost { my $a; sub middle { sub { $a } } } |
1202 | |
1203 | If the anonymous subroutine is called or referenced (directly or |
1204 | indirectly) from the outermost subroutine, it will share the variable |
1205 | as you would expect. But if the anonymous subroutine is called or |
1206 | referenced when the outermost subroutine is not active, it will see |
1207 | the value of the shared variable as it was before and during the |
1208 | *first* call to the outermost subroutine, which is probably not what |
1209 | you want. |
1210 | |
1211 | In these circumstances, it is usually best to make the middle |
1212 | subroutine anonymous, using the C<sub {}> syntax. Perl has specific |
1213 | support for shared variables in nested anonymous subroutines; a named |
1214 | subroutine in between interferes with this feature. |
1215 | |
1216 | =item Variable "%s" will not stay shared |
1217 | |
1218 | (W) An inner (nested) I<named> subroutine is referencing a lexical |
1219 | variable defined in an outer subroutine. |
1220 | |
1221 | When the inner subroutine is called, it will probably see the value of |
1222 | the outer subroutine's variable as it was before and during the |
1223 | *first* call to the outer subroutine; in this case, after the first |
1224 | call to the outer subroutine is complete, the inner and outer |
1225 | subroutines will no longer share a common value for the variable. In |
1226 | other words, the variable will no longer be shared. |
1227 | |
1228 | Furthermore, if the outer subroutine is anonymous and references a |
1229 | lexical variable outside itself, then the outer and inner subroutines |
1230 | will I<never> share the given variable. |
1231 | |
1232 | This problem can usually be solved by making the inner subroutine |
1233 | anonymous, using the C<sub {}> syntax. When inner anonymous subs that |
1234 | reference variables in outer subroutines are called or referenced, |
54310121 |
1235 | they are automatically rebound to the current values of such |
774d564b |
1236 | variables. |
1237 | |
1238 | =item Warning: something's wrong |
1239 | |
1240 | (W) You passed warn() an empty string (the equivalent of C<warn "">) or |
1241 | you called it with no args and C<$_> was empty. |
1242 | |
54310121 |
1243 | =item Ill-formed logical name |%s| in prime_env_iter |
1244 | |
1245 | (W) A warning peculiar to VMS. A logical name was encountered when preparing |
1246 | to iterate over %ENV which violates the syntactic rules governing logical |
1247 | names. Since it cannot be translated normally, it is skipped, and will not |
1248 | appear in %ENV. This may be a benign occurrence, as some software packages |
1249 | might directly modify logical name tables and introduce nonstandard names, |
1250 | or it may indicate that a logical name table has been corrupted. |
1251 | |
774d564b |
1252 | =item Got an error from DosAllocMem |
5f05dabc |
1253 | |
774d564b |
1254 | (P) An error peculiar to OS/2. Most probably you're using an obsolete |
1255 | version of Perl, and this should not happen anyway. |
5f05dabc |
1256 | |
1257 | =item Malformed PERLLIB_PREFIX |
1258 | |
dc848c6f |
1259 | (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form |
5f05dabc |
1260 | |
1261 | prefix1;prefix2 |
1262 | |
1263 | or |
1264 | |
1265 | prefix1 prefix2 |
1266 | |
dc848c6f |
1267 | with nonempty prefix1 and prefix2. If C<prefix1> is indeed a prefix |
1268 | of a builtin library search path, prefix2 is substituted. The error |
1269 | may appear if components are not found, or are too long. See |
1270 | "PERLLIB_PREFIX" in F<README.os2>. |
5f05dabc |
1271 | |
1272 | =item PERL_SH_DIR too long |
1273 | |
1274 | (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the |
dc848c6f |
1275 | C<sh>-shell in. See "PERL_SH_DIR" in F<README.os2>. |
5f05dabc |
1276 | |
1277 | =item Process terminated by SIG%s |
1278 | |
1279 | (W) This is a standard message issued by OS/2 applications, while *nix |
dc848c6f |
1280 | applications die in silence. It is considered a feature of the OS/2 |
1281 | port. One can easily disable this by appropriate sighandlers, see |
1282 | L<perlipc/"Signals">. See also "Process terminated by SIGTERM/SIGINT" |
1283 | in F<README.os2>. |
5f05dabc |
1284 | |
1285 | =back |
1286 | |
1287 | =head1 BUGS |
1288 | |
774d564b |
1289 | If you find what you think is a bug, you might check the headers of |
1290 | recently posted articles in the comp.lang.perl.misc newsgroup. |
1291 | There may also be information at http://www.perl.com/perl/, the Perl |
1292 | Home Page. |
5f05dabc |
1293 | |
1294 | If you believe you have an unreported bug, please run the B<perlbug> |
9607fc9c |
1295 | program included with your release. Make sure you trim your bug down |
1296 | to a tiny but sufficient test case. Your bug report, along with the |
1297 | output of C<perl -V>, will be sent off to <F<perlbug@perl.com>> to be |
1298 | analysed by the Perl porting team. |
5f05dabc |
1299 | |
1300 | =head1 SEE ALSO |
1301 | |
1302 | The F<Changes> file for exhaustive details on what changed. |
1303 | |
1304 | The F<INSTALL> file for how to build Perl. This file has been |
1305 | significantly updated for 5.004, so even veteran users should |
1306 | look through it. |
1307 | |
1308 | The F<README> file for general stuff. |
1309 | |
1310 | The F<Copying> file for copyright information. |
1311 | |
1312 | =head1 HISTORY |
1313 | |
1314 | Constructed by Tom Christiansen, grabbing material with permission |
1315 | from innumerable contributors, with kibitzing by more than a few Perl |
1316 | porters. |
1317 | |
2ae324a7 |
1318 | Last update: Sat Mar 8 19:51:26 EST 1997 |