1Error(3) User Contributed Perl Documentation Error(3)
2
6 Error - Error/exception handling in an OO-ish way
7
9 Using the "Error" module is no longer recommended due to the black-
10 magical nature of its syntactic sugar, which often tends to break. Its
11 maintainers have stopped actively writing code that uses it, and
12 discourage people from doing so. See the "SEE ALSO" section below for
13 better recommendations.
14
16 use Error qw(:try);
17 throw Error::Simple( "A simple error");
19 sub xyz {
21 ...
22 record Error::Simple("A simple error")
23 and return;
24 }
25 unlink($file) or throw Error::Simple("$file: $!",$!);
27 try {
29 do_some_stuff();
30 die "error!" if $condition;
31 throw Error::Simple "Oops!" if $other_condition;
32 }
33 catch Error::IO with {
34 my $E = shift;
35 print STDERR "File ", $E->{'-file'}, " had a problem\n";
36 }
37 except {
38 my $E = shift;
39 my $general_handler=sub {send_message $E->{-description}};
40 return {
41 UserException1 => $general_handler,
42 UserException2 => $general_handler
43 };
44 }
45 otherwise {
46 print STDERR "Well I don't know what to say\n";
47 }
48 finally {
49 close_the_garage_door_already(); # Should be reliable
50 }; # Don't forget the trailing ; or you might be surprised
51
53 The "Error" package provides two interfaces. Firstly "Error" provides a
54 procedural interface to exception handling. Secondly "Error" is a base
55 class for errors/exceptions that can either be thrown, for subsequent
56 catch, or can simply be recorded.
57 Errors in the class "Error" should not be thrown directly, but the user
59 should throw errors from a sub-class of "Error".
60
62 "Error" exports subroutines to perform exception handling. These will
63 be exported if the ":try" tag is used in the "use" line.
64 try BLOCK CLAUSES
66 "try" is the main subroutine called by the user. All other
67 subroutines exported are clauses to the try subroutine.
68 The BLOCK will be evaluated and, if no error is throw, try will
70 return the result of the block.
71 "CLAUSES" are the subroutines below, which describe what to do in
73 the event of an error being thrown within BLOCK.
74 catch CLASS with BLOCK
76 This clauses will cause all errors that satisfy "$err->isa(CLASS)"
77 to be caught and handled by evaluating "BLOCK".
78 "BLOCK" will be passed two arguments. The first will be the error
80 being thrown. The second is a reference to a scalar variable. If
81 this variable is set by the catch block then, on return from the
82 catch block, try will continue processing as if the catch block was
83 never found. The error will also be available in $@.
84 To propagate the error the catch block may call "$err->throw"
86 If the scalar reference by the second argument is not set, and the
88 error is not thrown. Then the current try block will return with
89 the result from the catch block.
90 except BLOCK
92 When "try" is looking for a handler, if an except clause is found
93 "BLOCK" is evaluated. The return value from this block should be a
94 HASHREF or a list of key-value pairs, where the keys are class
95 names and the values are CODE references for the handler of errors
96 of that type.
97 otherwise BLOCK
99 Catch any error by executing the code in "BLOCK"
100 When evaluated "BLOCK" will be passed one argument, which will be
102 the error being processed. The error will also be available in $@.
103 Only one otherwise block may be specified per try block
105 finally BLOCK
107 Execute the code in "BLOCK" either after the code in the try block
108 has successfully completed, or if the try block throws an error
109 then "BLOCK" will be executed after the handler has completed.
110 If the handler throws an error then the error will be caught, the
112 finally block will be executed and the error will be re-thrown.
113 Only one finally block may be specified per try block
115
117 Moose exports a keyword called "with" which clashes with Error's. This
118 example returns a prototype mismatch error:
119 package MyTest;
121 use warnings;
123 use Moose;
124 use Error qw(:try);
125 (Thanks to "maik.hentsche@amd.com" for the report.).
127
129 CONSTRUCTORS
130 The "Error" object is implemented as a HASH. This HASH is initialized
131 with the arguments that are passed to it's constructor. The elements
132 that are used by, or are retrievable by the "Error" class are listed
133 below, other classes may add to these.
134 -file
136 -line
137 -text
138 -value
139 -object
140 If "-file" or "-line" are not specified in the constructor arguments
142 then these will be initialized with the file name and line number where
143 the constructor was called from.
144 If the error is associated with an object then the object should be
146 passed as the "-object" argument. This will allow the "Error" package
147 to associate the error with the object.
148 The "Error" package remembers the last error created, and also the last
150 error associated with a package. This could either be the last error
151 created by a sub in that package, or the last error which passed an
152 object blessed into that package as the "-object" argument.
153 Error->new()
155 See the Error::Simple documentation.
156 throw ( [ ARGS ] )
158 Create a new "Error" object and throw an error, which will be
159 caught by a surrounding "try" block, if there is one. Otherwise it
160 will cause the program to exit.
161 "throw" may also be called on an existing error to re-throw it.
163 with ( [ ARGS ] )
165 Create a new "Error" object and returns it. This is defined for
166 syntactic sugar, eg
167 die with Some::Error ( ... );
169 record ( [ ARGS ] )
171 Create a new "Error" object and returns it. This is defined for
172 syntactic sugar, eg
173 record Some::Error ( ... )
175 and return;
176 STATIC METHODS
178 prior ( [ PACKAGE ] )
179 Return the last error created, or the last error associated with
180 "PACKAGE"
181 flush ( [ PACKAGE ] )
183 Flush the last error created, or the last error associated with
184 "PACKAGE".It is necessary to clear the error stack before exiting
185 the package or uncaught errors generated using "record" will be
186 reported.
187 $Error->flush;
189 OBJECT METHODS
191 stacktrace
192 If the variable $Error::Debug was non-zero when the error was
193 created, then "stacktrace" returns a string created by calling
194 "Carp::longmess". If the variable was zero the "stacktrace" returns
195 the text of the error appended with the filename and line number of
196 where the error was created, providing the text does not end with a
197 newline.
198 object
200 The object this error was associated with
201 file
203 The file where the constructor of this error was called from
204 line
206 The line where the constructor of this error was called from
207 text
209 The text of the error
210 $err->associate($obj)
212 Associates an error with an object to allow error propagation. I.e:
213 $ber->encode(...) or
215 return Error->prior($ber)->associate($ldap);
216 OVERLOAD METHODS
218 stringify
219 A method that converts the object into a string. This method may
220 simply return the same as the "text" method, or it may append more
221 information. For example the file name and line number.
222 By default this method returns the "-text" argument that was passed
224 to the constructor, or the string "Died" if none was given.
225 value
227 A method that will return a value that can be associated with the
228 error. For example if an error was created due to the failure of a
229 system call, then this may return the numeric value of $! at the
230 time.
231 By default this method returns the "-value" argument that was
233 passed to the constructor.
234
236 Error::Simple
237 This class can be used to hold simple error strings and values. It's
238 constructor takes two arguments. The first is a text value, the second
239 is a numeric value. These values are what will be returned by the
240 overload methods.
241 If the text value ends with "at file line 1" as $@ strings do, then
243 this infomation will be used to set the "-file" and "-line" arguments
244 of the error object.
245 This class is used internally if an eval'd block die's with an error
247 that is a plain string. (Unless $Error::ObjectifyCallback is modified)
248
250 This variable holds a reference to a subroutine that converts errors
251 that are plain strings to objects. It is used by Error.pm to convert
252 textual errors to objects, and can be overrided by the user.
253 It accepts a single argument which is a hash reference to named
255 parameters. Currently the only named parameter passed is 'text' which
256 is the text of the error, but others may be available in the future.
257 For example the following code will cause Error.pm to throw objects of
259 the class MyError::Bar by default:
260 sub throw_MyError_Bar
262 {
263 my $args = shift;
264 my $err = MyError::Bar->new();
265 $err->{'MyBarText'} = $args->{'text'};
266 return $err;
267 }
268 {
270 local $Error::ObjectifyCallback = \&throw_MyError_Bar;
271 # Error handling here.
273 }
274
276 "Error" also provides handlers to extend the output of the "warn()"
277 perl function, and to handle the printing of a thrown "Error" that is
278 not caught or otherwise handled. These are not installed by default,
279 but are requested using the ":warndie" tag in the "use" line.
280 use Error qw( :warndie );
282 These new error handlers are installed in $SIG{__WARN__} and
284 $SIG{__DIE__}. If these handlers are already defined when the tag is
285 imported, the old values are stored, and used during the new code.
286 Thus, to arrange for custom handling of warnings and errors, you will
287 need to perform something like the following:
288 BEGIN {
290 $SIG{__WARN__} = sub {
291 print STDERR "My special warning handler: $_[0]"
292 };
293 }
294 use Error qw( :warndie );
296 Note that setting $SIG{__WARN__} after the ":warndie" tag has been
298 imported will overwrite the handler that "Error" provides. If this
299 cannot be avoided, then the tag can be explicitly "import"ed later
300 use Error;
302 $SIG{__WARN__} = ...;
304 import Error qw( :warndie );
306 EXAMPLE
308 The "__DIE__" handler turns messages such as
309 Can't call method "foo" on an undefined value at examples/warndie.pl line 16.
311 into
313 Unhandled perl error caught at toplevel:
315 Can't call method "foo" on an undefined value
317 Thrown from: examples/warndie.pl:16
319 Full stack trace:
321 main::inner('undef') called at examples/warndie.pl line 20
323 main::outer('undef') called at examples/warndie.pl line 23
324
326 See Exception::Class for a different module providing Object-Oriented
327 exception handling, along with a convenient syntax for declaring
328 hierarchies for them. It doesn't provide Error's syntactic sugar of
329 "try { ... }", "catch { ... }", etc. which may be a good thing or a bad
330 thing based on what you want. (Because Error's syntactic sugar tends to
331 break.)
332 Error::Exception aims to combine Error and Exception::Class "with
334 correct stringification".
335 TryCatch and Try::Tiny are similar in concept to Error.pm only
337 providing a syntax that hopefully breaks less.
338
340 None, but that does not mean there are not any.
341
343 Graham Barr <gbarr@pobox.com>
344 The code that inspired me to write this was originally written by Peter
346 Seibel <peter@weblogic.com> and adapted by Jesse Glick
347 <jglick@sig.bsh.com>.
348 ":warndie" handlers added by Paul Evans <leonerd@leonerd.org.uk>
350
352 Shlomi Fish <shlomif@iglu.org.il>
353
355 Arun Kumar U <u_arunkumar@yahoo.com>
356
358 Copyright (c) 1997-8 Graham Barr. All rights reserved. This program
359 is free software; you can redistribute it and/or modify it under the
360 same terms as Perl itself.
361perl v5.12.0 2010-05-01 Error(3)