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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 | |
21 | =head2 Compilation Option: Binary Compatibility With 5.003 |
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 New Opcode Module and Revised Safe Module |
31 | |
32 | A new Opcode module supports the creation, manipulation and |
33 | application of opcode masks. The revised Safe module has a new API |
34 | and is implemented using the new Opcode module. Please read the new |
35 | Opcode and Safe documentation. |
36 | |
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37 | =head2 Internal Change: FileHandle Deprecated |
38 | |
39 | Filehandles are now stored internally as type IO::Handle. |
40 | Although C<use FileHandle> and C<*STDOUT{FILEHANDLE}> |
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41 | are still supported for backwards compatibility, |
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42 | C<use IO::Handle> (or C<IO::Seekable> or C<IO::File>) and |
43 | C<*STDOUT{IO}> are the way of the future. |
44 | |
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45 | =head2 Internal Change: PerlIO internal IO abstraction interface |
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46 | |
47 | It is now possible to build Perl with AT&T's sfio IO package |
48 | instead of stdio. See L<perlapio> for more details, and |
49 | the F<INSTALL> file for how to use it. |
50 | |
51 | =head2 New and Changed Built-in Variables |
52 | |
53 | =over |
54 | |
55 | =item $^E |
56 | |
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57 | Extended error message on some platforms. (Also known as |
58 | $EXTENDED_OS_ERROR if you C<use English>). |
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59 | |
60 | =item $^H |
61 | |
62 | The current set of syntax checks enabled by C<use strict>. See the |
63 | documentation of C<strict> for more details. Not actually new, but |
64 | newly documented. |
65 | Because it is intended for internal use by Perl core components, |
66 | there is no C<use English> long name for this variable. |
67 | |
68 | =item $^M |
69 | |
70 | By default, running out of memory it is not trappable. However, if |
71 | compiled for this, Perl may use the contents of C<$^M> as an emergency |
72 | pool after die()ing with this message. Suppose that your Perl were |
73 | compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then |
74 | |
75 | $^M = 'a' x (1<<16); |
76 | |
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77 | would allocate a 64K buffer for use when in emergency. |
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78 | See the F<INSTALL> file for information on how to enable this option. |
79 | As a disincentive to casual use of this advanced feature, |
80 | there is no C<use English> long name for this variable. |
81 | |
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82 | =item $^S |
83 | |
84 | The status returned by the last pipe close, back-tick (C<``>) command, or |
85 | system() operator, in the native system format. On UNIX and UNIX-like |
86 | systems, C<$^S> is a synonym for C<$?>. Elsewhere, C<$^S> can be used to |
87 | determine aspects of child status that are system-specific. Check C<$^O> |
88 | before using this variable. (Mnemonic: System-Specific Subprocess Status. |
89 | Also known as $SYSTEM_CHILD_STATUS if you C<use English>.) |
90 | |
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91 | =back |
92 | |
93 | =head2 New and Changed Built-in Functions |
94 | |
95 | =over |
96 | |
97 | =item delete on slices |
98 | |
99 | This now works. (e.g. C<delete @ENV{'PATH', 'MANPATH'}>) |
100 | |
101 | =item flock |
102 | |
103 | is now supported on more platforms, and prefers fcntl |
104 | to lockf when emulating. |
105 | |
106 | =item keys as an lvalue |
107 | |
108 | As an lvalue, C<keys> allows you to increase the number of hash buckets |
109 | allocated for the given associative array. This can gain you a measure |
110 | of efficiency if you know the hash is going to get big. (This is |
111 | similar to pre-extending an array by assigning a larger number to |
112 | $#array.) If you say |
113 | |
114 | keys %hash = 200; |
115 | |
116 | then C<%hash> will have at least 200 buckets allocated for it. These |
117 | buckets will be retained even if you do C<%hash = ()>; use C<undef |
118 | %hash> if you want to free the storage while C<%hash> is still in scope. |
119 | You can't shrink the number of buckets allocated for the hash using |
120 | C<keys> in this way (but you needn't worry about doing this by accident, |
121 | as trying has no effect). |
122 | |
123 | =item my() in Control Structures |
124 | |
125 | You can now use my() (with or without the parentheses) in the control |
126 | expressions of control structures such as: |
127 | |
128 | while (my $line = <>) { |
129 | $line = lc $line; |
130 | } continue { |
131 | print $line; |
132 | } |
133 | |
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134 | if ((my $answer = <STDIN>) =~ /^y(es)?$/i) { |
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135 | user_agrees(); |
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136 | } elsif ($answer =~ /^n(o)?$/i) { |
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137 | user_disagrees(); |
138 | } else { |
139 | chomp $answer; |
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140 | die "`$answer' is neither `yes' nor `no'"; |
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141 | } |
142 | |
143 | Also, you can declare a foreach loop control variable as lexical by |
144 | preceding it with the word "my". For example, in: |
145 | |
146 | foreach my $i (1, 2, 3) { |
147 | some_function(); |
148 | } |
149 | |
150 | $i is a lexical variable, and the scope of $i extends to the end of |
151 | the loop, but not beyond it. |
152 | |
153 | Note that you still cannot use my() on global punctuation variables |
154 | such as $_ and the like. |
155 | |
156 | =item unpack() and pack() |
157 | |
158 | A new format 'w' represents a BER compressed integer (as defined in |
159 | ASN.1). Its format is a sequence of one or more bytes, each of which |
160 | provides seven bits of the total value, with the most significant |
161 | first. Bit eight of each byte is set, except for the last byte, in |
162 | which bit eight is clear. |
163 | |
164 | =item use VERSION |
165 | |
166 | If the first argument to C<use> is a number, it is treated as a version |
167 | number instead of a module name. If the version of the Perl interpreter |
168 | is less than VERSION, then an error message is printed and Perl exits |
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169 | immediately. Because C<use> occurs at compile time, this check happens |
170 | immediately during the compilation process, unlike C<require VERSION>, |
171 | which waits until run-time for the check. This is often useful if you |
172 | need to check the current Perl version before C<use>ing library modules |
173 | which have changed in incompatible ways from older versions of Perl. |
174 | (We try not to do this more than we have to.) |
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175 | |
176 | =item use Module VERSION LIST |
177 | |
178 | If the VERSION argument is present between Module and LIST, then the |
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179 | C<use> will call the VERSION method in class Module with the given |
180 | version as an argument. The default VERSION method, inherited from |
181 | the Universal class, croaks if the given version is larger than the |
182 | value of the variable $Module::VERSION. (Note that there is not a |
183 | comma after VERSION!) |
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184 | |
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185 | This version-checking mechanism is similar to the one currently used |
186 | in the Exporter module, but it is faster and can be used with modules |
187 | that don't use the Exporter. It is the recommended method for new |
188 | code. |
189 | |
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190 | =item prototype(FUNCTION) |
191 | |
192 | Returns the prototype of a function as a string (or C<undef> if the |
193 | function has no prototype). FUNCTION is a reference to or the name of the |
194 | function whose prototype you want to retrieve. |
195 | (Not actually new; just never documented before.) |
196 | |
197 | =item $_ as Default |
198 | |
199 | Functions documented in the Camel to default to $_ now in |
200 | fact do, and all those that do are so documented in L<perlfunc>. |
201 | |
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202 | =item C<m//g> does not trigger a pos() reset on failure |
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203 | |
204 | The C<m//g> match iteration construct used to reset the iteration |
205 | when it failed to match (so that the next C<m//g> match would start at |
206 | the beginning of the string). You now have to explicitly do a |
207 | C<pos $str = 0;> to reset the "last match" position, or modify the |
208 | string in some way. This change makes it practical to chain C<m//g> |
209 | matches together in conjunction with ordinary matches using the C<\G> |
210 | zero-width assertion. See L<perlop> and L<perlre>. |
211 | |
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212 | =item nested C<sub{}> closures work now |
213 | |
214 | Prior to the 5.004 release, nested anonymous functions |
215 | didn't work right. They do now. |
216 | |
217 | =item formats work right on changing lexicals |
218 | |
219 | Just like anonymous functions that contain lexical variables |
220 | that change (like a lexical index variable for a C<foreach> loop), |
221 | formats now work properly. For example, this silently failed |
222 | before, and is fine now: |
223 | |
224 | my $i; |
225 | foreach $i ( 1 .. 10 ) { |
226 | format = |
227 | my i is @# |
228 | $i |
229 | . |
230 | write; |
231 | } |
232 | |
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233 | =back |
234 | |
235 | =head2 New Built-in Methods |
236 | |
237 | The C<UNIVERSAL> package automatically contains the following methods that |
238 | are inherited by all other classes: |
239 | |
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240 | =over |
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241 | |
242 | =item isa(CLASS) |
243 | |
244 | C<isa> returns I<true> if its object is blessed into a sub-class of C<CLASS> |
245 | |
246 | C<isa> is also exportable and can be called as a sub with two arguments. This |
247 | allows the ability to check what a reference points to. Example: |
248 | |
249 | use UNIVERSAL qw(isa); |
250 | |
251 | if(isa($ref, 'ARRAY')) { |
252 | ... |
253 | } |
254 | |
255 | =item can(METHOD) |
256 | |
257 | C<can> checks to see if its object has a method called C<METHOD>, |
258 | if it does then a reference to the sub is returned; if it does not then |
259 | I<undef> is returned. |
260 | |
261 | =item VERSION( [NEED] ) |
262 | |
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263 | C<VERSION> returns the version number of the class (package). If the |
264 | NEED argument is given then it will check that the current version (as |
265 | defined by the $VERSION variable in the given package) not less than |
266 | NEED; it will die if this is not the case. This method is normally |
267 | called as a class method. This method is called automatically by the |
268 | C<VERSION> form of C<use>. |
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269 | |
270 | use A 1.2 qw(some imported subs); |
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271 | # implies: |
272 | A->VERSION(1.2); |
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273 | |
274 | =item class() |
275 | |
276 | C<class> returns the class name of its object. |
277 | |
278 | =item is_instance() |
279 | |
280 | C<is_instance> returns true if its object is an instance of some |
281 | class, false if its object is the class (package) itself. Example |
282 | |
283 | A->is_instance(); # False |
284 | |
285 | $var = 'A'; |
286 | $var->is_instance(); # False |
287 | |
288 | $ref = bless [], 'A'; |
289 | $ref->is_instance(); # True |
290 | |
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291 | This can be useful for methods that wish to easily distinguish |
292 | whether they were invoked as class or as instance methods. |
293 | |
294 | sub some_meth { |
295 | my $classname = shift; |
296 | if ($classname->is_instance()) { |
297 | die "unexpectedly called as instance not class method"; |
298 | } |
299 | ..... |
300 | } |
301 | |
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302 | =back |
303 | |
304 | B<NOTE:> C<can> directly uses Perl's internal code for method lookup, and |
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305 | C<isa> uses a very similar method and caching strategy. This may cause |
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306 | strange effects if the Perl code dynamically changes @ISA in any package. |
307 | |
308 | You may add other methods to the UNIVERSAL class via Perl or XS code. |
309 | You do not need to C<use UNIVERSAL> in order to make these methods |
310 | available to your program. This is necessary only if you wish to |
311 | have C<isa> available as a plain subroutine in the current package. |
312 | |
313 | =head2 TIEHANDLE Now Supported |
314 | |
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315 | See L<perltie> for other kinds of tie()s. |
316 | |
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317 | =over |
318 | |
319 | =item TIEHANDLE classname, LIST |
320 | |
321 | This is the constructor for the class. That means it is expected to |
322 | return an object of some sort. The reference can be used to |
323 | hold some internal information. |
324 | |
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325 | sub TIEHANDLE { |
326 | print "<shout>\n"; |
327 | my $i; |
328 | return bless \$i, shift; |
329 | } |
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330 | |
331 | =item PRINT this, LIST |
332 | |
333 | This method will be triggered every time the tied handle is printed to. |
334 | Beyond its self reference it also expects the list that was passed to |
335 | the print function. |
336 | |
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337 | sub PRINT { |
338 | $r = shift; |
339 | $$r++; |
340 | return print join( $, => map {uc} @_), $\; |
341 | } |
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342 | |
343 | =item READLINE this |
344 | |
345 | This method will be called when the handle is read from. The method |
346 | should return undef when there is no more data. |
347 | |
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348 | sub READLINE { |
349 | $r = shift; |
350 | return "PRINT called $$r times\n"; |
351 | } |
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352 | |
353 | =item DESTROY this |
354 | |
355 | As with the other types of ties, this method will be called when the |
356 | tied handle is about to be destroyed. This is useful for debugging and |
357 | possibly for cleaning up. |
358 | |
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359 | sub DESTROY { |
360 | print "</shout>\n"; |
361 | } |
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362 | |
363 | =back |
364 | |
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365 | =item Efficiency Enhancements |
366 | |
367 | All hash keys with the same string are only allocated once, so |
368 | even if you have 100 copies of the same hash, the immutable keys |
369 | never have to be re-allocated. |
370 | |
371 | Functions that have an empty prototype and that do nothing but return |
372 | a fixed value are now inlined (e.g. C<sub PI () { 3.14159 }>). |
373 | |
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374 | =head1 Pragmata |
375 | |
376 | Three new pragmatic modules exist: |
377 | |
378 | =over |
379 | |
380 | =item use blib |
381 | |
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382 | =item use blib 'dir' |
383 | |
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384 | Looks for MakeMaker-like I<'blib'> directory structure starting in |
385 | I<dir> (or current directory) and working back up to five levels of |
386 | parent directories. |
387 | |
388 | Intended for use on command line with B<-M> option as a way of testing |
389 | arbitrary scripts against an uninstalled version of a package. |
390 | |
391 | =item use locale |
392 | |
393 | Tells the compiler to enable (or disable) the use of POSIX locales for |
394 | built-in operations. |
395 | |
396 | When C<use locale> is in effect, the current LC_CTYPE locale is used |
397 | for regular expressions and case mapping; LC_COLLATE for string |
398 | ordering; and LC_NUMERIC for numeric formating in printf and sprintf |
399 | (but B<not> in print). LC_NUMERIC is always used in write, since |
400 | lexical scoping of formats is problematic at best. |
401 | |
402 | Each C<use locale> or C<no locale> affects statements to the end of |
403 | the enclosing BLOCK or, if not inside a BLOCK, to the end of the |
404 | current file. Locales can be switched and queried with |
405 | POSIX::setlocale(). |
406 | |
407 | See L<perllocale> for more information. |
408 | |
409 | =item use ops |
410 | |
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411 | Disable unsafe opcodes, or any named opcodes, when compiling Perl code. |
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412 | |
413 | =back |
414 | |
415 | =head1 Modules |
416 | |
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417 | =head2 Installation Directories |
418 | |
419 | The I<installperl> script now places the Perl source files for |
420 | extensions in the architecture-specific library directory, which is |
421 | where the shared libraries for extensions have always been. This |
422 | change is intended to allow administrators to keep the Perl 5.004 |
423 | library directory unchanged from a previous version, without running |
424 | the risk of binary incompatibility between extensions' Perl source and |
425 | shared libraries. |
426 | |
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427 | =head2 Fcntl |
428 | |
429 | New constants in the existing Fcntl modules are now supported, |
430 | provided that your operating system happens to support them: |
431 | |
432 | F_GETOWN F_SETOWN |
433 | O_ASYNC O_DEFER O_DSYNC O_FSYNC O_SYNC |
434 | O_EXLOCK O_SHLOCK |
435 | |
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436 | These constants are intended for use with the Perl operators sysopen() |
437 | and fcntl() and the basic database modules like SDBM_File. For the |
438 | exact meaning of these and other Fcntl constants please refer to your |
439 | operating system's documentation for fcntl() and open(). |
440 | |
441 | In addition, the Fcntl module now provides these constants for use |
442 | with the Perl operator flock(): |
443 | |
444 | LOCK_SH LOCK_EX LOCK_NB LOCK_UN |
445 | |
446 | These constants are defined in all environments (because where there is |
447 | no flock() system call, Perl emulates it). However, for historical |
448 | reasons, these constants are not exported unless they are explicitly |
449 | requested with the ":flock" tag (e.g. C<use Fcntl ':flock'>). |
450 | |
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451 | =head2 Module Information Summary |
452 | |
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453 | Brand new modules, arranged by topic rather than strictly |
454 | alphabetically: |
455 | |
456 | CPAN interface to Comprehensive Perl Archive Network |
457 | CPAN::FirstTime create a CPAN configuration file |
458 | CPAN::Nox run CPAN while avoiding compiled extensions |
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459 | |
460 | IO.pm Top-level interface to IO::* classes |
461 | IO/File.pm IO::File extension Perl module |
462 | IO/Handle.pm IO::Handle extension Perl module |
463 | IO/Pipe.pm IO::Pipe extension Perl module |
464 | IO/Seekable.pm IO::Seekable extension Perl module |
465 | IO/Select.pm IO::Select extension Perl module |
466 | IO/Socket.pm IO::Socket extension Perl module |
467 | |
468 | Opcode.pm Disable named opcodes when compiling Perl code |
469 | |
470 | ExtUtils/Embed.pm Utilities for embedding Perl in C programs |
471 | ExtUtils/testlib.pm Fixes up @INC to use just-built extension |
472 | |
473 | Fatal.pm Make do-or-die equivalents of functions |
474 | FindBin.pm Find path of currently executing program |
475 | |
476 | Class/Template.pm Structure/member template builder |
477 | File/stat.pm Object-oriented wrapper around CORE::stat |
478 | Net/hostent.pm Object-oriented wrapper around CORE::gethost* |
479 | Net/netent.pm Object-oriented wrapper around CORE::getnet* |
480 | Net/protoent.pm Object-oriented wrapper around CORE::getproto* |
481 | Net/servent.pm Object-oriented wrapper around CORE::getserv* |
482 | Time/gmtime.pm Object-oriented wrapper around CORE::gmtime |
483 | Time/localtime.pm Object-oriented wrapper around CORE::localtime |
484 | Time/tm.pm Perl implementation of "struct tm" for {gm,local}time |
485 | User/grent.pm Object-oriented wrapper around CORE::getgr* |
486 | User/pwent.pm Object-oriented wrapper around CORE::getpw* |
487 | |
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488 | Tie/RefHash.pm Base class for tied hashes with references as keys |
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489 | |
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490 | UNIVERSAL.pm Base class for *ALL* classes |
491 | |
492 | =head2 IO |
493 | |
494 | The IO module provides a simple mechanism to load all of the IO modules at one |
495 | go. Currently this includes: |
496 | |
497 | IO::Handle |
498 | IO::Seekable |
499 | IO::File |
500 | IO::Pipe |
501 | IO::Socket |
502 | |
503 | For more information on any of these modules, please see its |
504 | respective documentation. |
505 | |
506 | =head2 Math::Complex |
507 | |
508 | The Math::Complex module has been totally rewritten, and now supports |
509 | more operations. These are overloaded: |
510 | |
511 | + - * / ** <=> neg ~ abs sqrt exp log sin cos atan2 "" (stringify) |
512 | |
513 | And these functions are now exported: |
514 | |
515 | pi i Re Im arg |
516 | log10 logn cbrt root |
517 | tan cotan asin acos atan acotan |
518 | sinh cosh tanh cotanh asinh acosh atanh acotanh |
519 | cplx cplxe |
520 | |
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521 | =head2 DB_File |
522 | |
523 | There have been quite a few changes made to DB_File. Here are a few of |
524 | the highlights: |
525 | |
526 | =over |
527 | |
528 | =item * |
529 | |
530 | Fixed a handful of bugs. |
531 | |
532 | =item * |
533 | |
534 | By public demand, added support for the standard hash function exists(). |
535 | |
536 | =item * |
537 | |
538 | Made it compatible with Berkeley DB 1.86. |
539 | |
540 | =item * |
541 | |
542 | Made negative subscripts work with RECNO interface. |
543 | |
544 | =item * |
545 | |
546 | Changed the default flags from O_RDWR to O_CREAT|O_RDWR and the default |
547 | mode from 0640 to 0666. |
548 | |
549 | =item * |
550 | |
551 | Made DB_File automatically import the open() constants (O_RDWR, |
552 | O_CREAT etc.) from Fcntl, if available. |
553 | |
554 | =item * |
555 | |
556 | Updated documentation. |
557 | |
558 | =back |
559 | |
560 | Refer to the HISTORY section in DB_File.pm for a complete list of |
561 | changes. Everything after DB_File 1.01 has been added since 5.003. |
562 | |
563 | =head2 Net::Ping |
564 | |
565 | Major rewrite - support added for both udp echo and real icmp pings. |
566 | |
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567 | =head2 Overridden Built-ins |
568 | |
569 | Many of the Perl built-ins returning lists now have |
570 | object-oriented overrides. These are: |
571 | |
572 | File::stat |
573 | Net::hostent |
574 | Net::netent |
575 | Net::protoent |
576 | Net::servent |
577 | Time::gmtime |
578 | Time::localtime |
579 | User::grent |
580 | User::pwent |
581 | |
582 | For example, you can now say |
583 | |
584 | use File::stat; |
585 | use User::pwent; |
586 | $his = (stat($filename)->st_uid == pwent($whoever)->pw_uid); |
587 | |
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588 | =head1 Utility Changes |
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589 | |
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590 | =head2 xsubpp |
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591 | |
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592 | =over |
593 | |
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594 | =item C<void> XSUBs now default to returning nothing |
595 | |
596 | Due to a documentation/implementation bug in previous versions of |
597 | Perl, XSUBs with a return type of C<void> have actually been |
598 | returning one value. Usually that value was the GV for the XSUB, |
599 | but sometimes it was some already freed or reused value, which would |
600 | sometimes lead to program failure. |
601 | |
602 | In Perl 5.004, if an XSUB is declared as returning C<void>, it |
603 | actually returns no value, i.e. an empty list (though there is a |
604 | backward-compatibility exception; see below). If your XSUB really |
605 | does return an SV, you should give it a return type of C<SV *>. |
606 | |
607 | For backward compatibility, I<xsubpp> tries to guess whether a |
608 | C<void> XSUB is really C<void> or if it wants to return an C<SV *>. |
609 | It does so by examining the text of the XSUB: if I<xsubpp> finds |
610 | what looks like an assignment to C<ST(0)>, it assumes that the |
611 | XSUB's return type is really C<SV *>. |
5f05dabc |
612 | |
0a753a76 |
613 | =back |
614 | |
615 | =head1 C Language API Changes |
616 | |
617 | =over |
618 | |
619 | =item C<gv_fetchmethod> and C<perl_call_sv> |
620 | |
621 | The C<gv_fetchmethod> function finds a method for an object, just like |
622 | in Perl 5.003. The GV it returns may be a method cache entry. |
623 | However, in Perl 5.004, method cache entries are not visible to users; |
624 | therefore, they can no longer be passed directly to C<perl_call_sv>. |
625 | Instead, you should use the C<GvCV> macro on the GV to extract its CV, |
626 | and pass the CV to C<perl_call_sv>. |
627 | |
628 | The most likely symptom of passing the result of C<gv_fetchmethod> to |
629 | C<perl_call_sv> is Perl's producing an "Undefined subroutine called" |
630 | error on the I<second> call to a given method (since there is no cache |
631 | on the first call). |
632 | |
633 | =back |
634 | |
5f05dabc |
635 | =head1 Documentation Changes |
636 | |
637 | Many of the base and library pods were updated. These |
638 | new pods are included in section 1: |
639 | |
0a753a76 |
640 | =over |
5f05dabc |
641 | |
774d564b |
642 | =item L<perldelta> |
5f05dabc |
643 | |
71be2cbc |
644 | This document. |
5f05dabc |
645 | |
71be2cbc |
646 | =item L<perllocale> |
5f05dabc |
647 | |
71be2cbc |
648 | Locale support (internationalization and localization). |
5f05dabc |
649 | |
650 | =item L<perltoot> |
651 | |
652 | Tutorial on Perl OO programming. |
653 | |
71be2cbc |
654 | =item L<perlapio> |
655 | |
656 | Perl internal IO abstraction interface. |
657 | |
5f05dabc |
658 | =item L<perldebug> |
659 | |
660 | Although not new, this has been massively updated. |
661 | |
662 | =item L<perlsec> |
663 | |
664 | Although not new, this has been massively updated. |
665 | |
666 | =back |
667 | |
668 | =head1 New Diagnostics |
669 | |
670 | Several new conditions will trigger warnings that were |
671 | silent before. Some only affect certain platforms. |
774d564b |
672 | The following new warnings and errors outline these. |
673 | These messages are classified as follows (listed in |
674 | increasing order of desperation): |
675 | |
676 | (W) A warning (optional). |
677 | (D) A deprecation (optional). |
678 | (S) A severe warning (mandatory). |
679 | (F) A fatal error (trappable). |
680 | (P) An internal error you should never see (trappable). |
681 | (X) A very fatal error (non-trappable). |
682 | (A) An alien error message (not generated by Perl). |
5f05dabc |
683 | |
0a753a76 |
684 | =over |
5f05dabc |
685 | |
686 | =item "my" variable %s masks earlier declaration in same scope |
687 | |
688 | (S) A lexical variable has been redeclared in the same scope, effectively |
689 | eliminating all access to the previous instance. This is almost always |
690 | a typographical error. Note that the earlier variable will still exist |
691 | until the end of the scope or until all closure referents to it are |
692 | destroyed. |
693 | |
774d564b |
694 | =item %s argument is not a HASH element or slice |
695 | |
696 | (F) The argument to delete() must be either a hash element, such as |
697 | |
698 | $foo{$bar} |
699 | $ref->[12]->{"susie"} |
700 | |
701 | or a hash slice, such as |
702 | |
703 | @foo{$bar, $baz, $xyzzy} |
704 | @{$ref->[12]}{"susie", "queue"} |
705 | |
5f05dabc |
706 | =item Allocation too large: %lx |
707 | |
708 | (X) You can't allocate more than 64K on an MSDOS machine. |
709 | |
710 | =item Allocation too large |
711 | |
712 | (F) You can't allocate more than 2^31+"small amount" bytes. |
713 | |
714 | =item Attempt to free non-existent shared string |
715 | |
716 | (P) Perl maintains a reference counted internal table of strings to |
717 | optimize the storage and access of hash keys and other strings. This |
718 | indicates someone tried to decrement the reference count of a string |
719 | that can no longer be found in the table. |
720 | |
721 | =item Attempt to use reference as lvalue in substr |
722 | |
723 | (W) You supplied a reference as the first argument to substr() used |
724 | as an lvalue, which is pretty strange. Perhaps you forgot to |
725 | dereference it first. See L<perlfunc/substr>. |
726 | |
727 | =item Unsupported function fork |
728 | |
729 | (F) Your version of executable does not support forking. |
730 | |
731 | Note that under some systems, like OS/2, there may be different flavors of |
732 | Perl executables, some of which may support fork, some not. Try changing |
733 | the name you call Perl by to C<perl_>, C<perl__>, and so on. |
734 | |
735 | =item Ill-formed logical name |%s| in prime_env_iter |
736 | |
737 | (W) A warning peculiar to VMS. A logical name was encountered when preparing |
738 | to iterate over %ENV which violates the syntactic rules governing logical |
739 | names. Since it cannot be translated normally, it is skipped, and will not |
740 | appear in %ENV. This may be a benign occurrence, as some software packages |
741 | might directly modify logical name tables and introduce non-standard names, |
742 | or it may indicate that a logical name table has been corrupted. |
743 | |
774d564b |
744 | =item Can't use bareword ("%s") as %s ref while "strict refs" in use |
745 | |
746 | (F) Only hard references are allowed by "strict refs". Symbolic references |
747 | are disallowed. See L<perlref>. |
748 | |
749 | =item Constant subroutine %s redefined |
750 | |
751 | (S) You redefined a subroutine which had previously been eligible for |
752 | inlining. See L<perlsub/"Constant Functions"> for commentary and |
753 | workarounds. |
754 | |
755 | =item Died |
756 | |
757 | (F) You passed die() an empty string (the equivalent of C<die "">) or |
758 | you called it with no args and both C<$@> and C<$_> were empty. |
759 | |
5f05dabc |
760 | =item Integer overflow in hex number |
761 | |
762 | (S) The literal hex number you have specified is too big for your |
763 | architecture. On a 32-bit architecture the largest hex literal is |
764 | 0xFFFFFFFF. |
765 | |
766 | =item Integer overflow in octal number |
767 | |
768 | (S) The literal octal number you have specified is too big for your |
769 | architecture. On a 32-bit architecture the largest octal literal is |
770 | 037777777777. |
771 | |
774d564b |
772 | =item Name "%s::%s" used only once: possible typo |
773 | |
774 | (W) Typographical errors often show up as unique variable names. |
775 | If you had a good reason for having a unique name, then just mention |
776 | it again somehow to suppress the message (the C<use vars> pragma is |
777 | provided for just this purpose). |
778 | |
5f05dabc |
779 | =item Null picture in formline |
780 | |
781 | (F) The first argument to formline must be a valid format picture |
782 | specification. It was found to be empty, which probably means you |
783 | supplied it an uninitialized value. See L<perlform>. |
784 | |
785 | =item Offset outside string |
786 | |
787 | (F) You tried to do a read/write/send/recv operation with an offset |
788 | pointing outside the buffer. This is difficult to imagine. |
789 | The sole exception to this is that C<sysread()>ing past the buffer |
790 | will extend the buffer and zero pad the new area. |
791 | |
774d564b |
792 | =item Stub found while resolving method `%s' overloading `%s' in package `%s' |
793 | |
794 | (P) Overloading resolution over @ISA tree may be broken by importing stubs. |
795 | Stubs should never be implicitely created, but explicit calls to C<can> |
796 | may break this. |
797 | |
798 | =item Cannot resolve method `%s' overloading `%s' in package `s' |
799 | |
800 | (P) Internal error trying to resolve overloading specified by a method |
801 | name (as opposed to a subroutine reference). |
802 | |
5f05dabc |
803 | =item Out of memory! |
804 | |
805 | (X|F) The malloc() function returned 0, indicating there was insufficient |
806 | remaining memory (or virtual memory) to satisfy the request. |
807 | |
808 | The request was judged to be small, so the possibility to trap it |
809 | depends on the way Perl was compiled. By default it is not trappable. |
810 | However, if compiled for this, Perl may use the contents of C<$^M> as |
811 | an emergency pool after die()ing with this message. In this case the |
812 | error is trappable I<once>. |
813 | |
814 | =item Out of memory during request for %s |
815 | |
816 | (F) The malloc() function returned 0, indicating there was insufficient |
817 | remaining memory (or virtual memory) to satisfy the request. However, |
818 | the request was judged large enough (compile-time default is 64K), so |
819 | a possibility to shut down by trapping this error is granted. |
820 | |
821 | =item Possible attempt to put comments in qw() list |
822 | |
774d564b |
823 | (W) qw() lists contain items separated by whitespace; as with literal |
824 | strings, comment characters are not ignored, but are instead treated |
825 | as literal data. (You may have used different delimiters than the |
826 | exclamation marks parentheses shown here; braces are also frequently |
827 | used.) |
828 | |
829 | You probably wrote something like this: |
5f05dabc |
830 | |
774d564b |
831 | @list = qw( |
832 | a # a comment |
5f05dabc |
833 | b # another comment |
774d564b |
834 | ); |
5f05dabc |
835 | |
836 | when you should have written this: |
837 | |
774d564b |
838 | @list = qw( |
839 | a |
5f05dabc |
840 | b |
774d564b |
841 | ); |
842 | |
843 | If you really want comments, build your list the |
844 | old-fashioned way, with quotes and commas: |
845 | |
846 | @list = ( |
847 | 'a', # a comment |
848 | 'b', # another comment |
849 | ); |
5f05dabc |
850 | |
851 | =item Possible attempt to separate words with commas |
852 | |
774d564b |
853 | (W) qw() lists contain items separated by whitespace; therefore commas |
854 | aren't needed to separate the items. (You may have used different |
855 | delimiters than the parentheses shown here; braces are also frequently |
856 | used.) |
5f05dabc |
857 | |
774d564b |
858 | You probably wrote something like this: |
5f05dabc |
859 | |
774d564b |
860 | qw! a, b, c !; |
861 | |
862 | which puts literal commas into some of the list items. Write it without |
863 | commas if you don't want them to appear in your data: |
864 | |
865 | qw! a b c !; |
5f05dabc |
866 | |
774d564b |
867 | =item Scalar value @%s{%s} better written as $%s{%s} |
868 | |
869 | (W) You've used a hash slice (indicated by @) to select a single element of |
870 | a hash. Generally it's better to ask for a scalar value (indicated by $). |
871 | The difference is that C<$foo{&bar}> always behaves like a scalar, both when |
872 | assigning to it and when evaluating its argument, while C<@foo{&bar}> behaves |
873 | like a list when you assign to it, and provides a list context to its |
874 | subscript, which can do weird things if you're expecting only one subscript. |
5f05dabc |
875 | |
876 | =item untie attempted while %d inner references still exist |
877 | |
878 | (W) A copy of the object returned from C<tie> (or C<tied>) was still |
879 | valid when C<untie> was called. |
880 | |
774d564b |
881 | =item Value of %s construct can be "0"; test with defined() |
882 | |
883 | (W) In a conditional expression, you used <HANDLE>, <*> (glob), or |
884 | C<readdir> as a boolean value. Each of these constructs can return a |
885 | value of "0"; that would make the conditional expression false, which |
886 | is probably not what you intended. When using these constructs in |
887 | conditional expressions, test their values with the C<defined> operator. |
888 | |
889 | =item Variable "%s" may be unavailable |
890 | |
891 | (W) An inner (nested) I<anonymous> subroutine is inside a I<named> |
892 | subroutine, and outside that is another subroutine; and the anonymous |
893 | (innermost) subroutine is referencing a lexical variable defined in |
894 | the outermost subroutine. For example: |
895 | |
896 | sub outermost { my $a; sub middle { sub { $a } } } |
897 | |
898 | If the anonymous subroutine is called or referenced (directly or |
899 | indirectly) from the outermost subroutine, it will share the variable |
900 | as you would expect. But if the anonymous subroutine is called or |
901 | referenced when the outermost subroutine is not active, it will see |
902 | the value of the shared variable as it was before and during the |
903 | *first* call to the outermost subroutine, which is probably not what |
904 | you want. |
905 | |
906 | In these circumstances, it is usually best to make the middle |
907 | subroutine anonymous, using the C<sub {}> syntax. Perl has specific |
908 | support for shared variables in nested anonymous subroutines; a named |
909 | subroutine in between interferes with this feature. |
910 | |
911 | =item Variable "%s" will not stay shared |
912 | |
913 | (W) An inner (nested) I<named> subroutine is referencing a lexical |
914 | variable defined in an outer subroutine. |
915 | |
916 | When the inner subroutine is called, it will probably see the value of |
917 | the outer subroutine's variable as it was before and during the |
918 | *first* call to the outer subroutine; in this case, after the first |
919 | call to the outer subroutine is complete, the inner and outer |
920 | subroutines will no longer share a common value for the variable. In |
921 | other words, the variable will no longer be shared. |
922 | |
923 | Furthermore, if the outer subroutine is anonymous and references a |
924 | lexical variable outside itself, then the outer and inner subroutines |
925 | will I<never> share the given variable. |
926 | |
927 | This problem can usually be solved by making the inner subroutine |
928 | anonymous, using the C<sub {}> syntax. When inner anonymous subs that |
929 | reference variables in outer subroutines are called or referenced, |
930 | they are automatically re-bound to the current values of such |
931 | variables. |
932 | |
933 | =item Warning: something's wrong |
934 | |
935 | (W) You passed warn() an empty string (the equivalent of C<warn "">) or |
936 | you called it with no args and C<$_> was empty. |
937 | |
938 | =item Got an error from DosAllocMem |
5f05dabc |
939 | |
774d564b |
940 | (P) An error peculiar to OS/2. Most probably you're using an obsolete |
941 | version of Perl, and this should not happen anyway. |
5f05dabc |
942 | |
943 | =item Malformed PERLLIB_PREFIX |
944 | |
945 | (F) An error peculiar to OS/2. PERLLIB_PREFIX should be of the form |
946 | |
947 | prefix1;prefix2 |
948 | |
949 | or |
950 | |
951 | prefix1 prefix2 |
952 | |
953 | with non-empty prefix1 and prefix2. If C<prefix1> is indeed a prefix of |
954 | a builtin library search path, prefix2 is substituted. The error may appear |
955 | if components are not found, or are too long. See L<perlos2/"PERLLIB_PREFIX">. |
956 | |
957 | =item PERL_SH_DIR too long |
958 | |
959 | (F) An error peculiar to OS/2. PERL_SH_DIR is the directory to find the |
960 | C<sh>-shell in. See L<perlos2/"PERL_SH_DIR">. |
961 | |
962 | =item Process terminated by SIG%s |
963 | |
964 | (W) This is a standard message issued by OS/2 applications, while *nix |
965 | applications die in silence. It is considered a feature of the OS/2 |
966 | port. One can easily disable this by appropriate sighandlers, see |
967 | L<perlipc/"Signals">. See L<perlos2/"Process terminated by SIGTERM/SIGINT">. |
968 | |
969 | =back |
970 | |
971 | =head1 BUGS |
972 | |
774d564b |
973 | If you find what you think is a bug, you might check the headers of |
974 | recently posted articles in the comp.lang.perl.misc newsgroup. |
975 | There may also be information at http://www.perl.com/perl/, the Perl |
976 | Home Page. |
5f05dabc |
977 | |
978 | If you believe you have an unreported bug, please run the B<perlbug> |
979 | program included with your release. Make sure you trim your bug |
980 | down to a tiny but sufficient test case. Your bug report, along |
981 | with the output of C<perl -V>, will be sent off to perlbug@perl.com |
982 | to be analysed by the Perl porting team. |
983 | |
984 | =head1 SEE ALSO |
985 | |
986 | The F<Changes> file for exhaustive details on what changed. |
987 | |
988 | The F<INSTALL> file for how to build Perl. This file has been |
989 | significantly updated for 5.004, so even veteran users should |
990 | look through it. |
991 | |
992 | The F<README> file for general stuff. |
993 | |
994 | The F<Copying> file for copyright information. |
995 | |
996 | =head1 HISTORY |
997 | |
998 | Constructed by Tom Christiansen, grabbing material with permission |
999 | from innumerable contributors, with kibitzing by more than a few Perl |
1000 | porters. |
1001 | |
44a8e56a |
1002 | Last update: Tue Jan 14 14:03:02 EST 1997 |