1Moose::Manual::ExceptioUnsse(r3)Contributed Perl DocumenMtoaotsieo:n:Manual::Exceptions(3)
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NAME

6       Moose::Manual::Exceptions - Moose's exceptions
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VERSION

9       version 2.2015
10

EXCEPTIONS IN MOOSE

12       Moose will throw an exception for all error conditions. This applies
13       both to code in the Moose core as well as to all code generated when a
14       class is made immutable. All exceptions are subclasses of the
15       "Moose::Exception" class.
16
17       Each type of error has its own unique subclass, and many subclasses
18       have additional attributes to provide more information about the
19       error's context, such as what classes or roles were involved.
20

EXCEPTION STRINGIFICATION

22       By default, Moose exceptions remove Moose internals from the stack
23       trace. If you set the "MOOSE_FULL_EXCEPTION" environment variable to a
24       true value, then the Moose internals will be included in the trace.
25

HANDLING MOOSE EXCEPTIONS

27       Because Moose's exceptions use the standard "die" mechanism, you are
28       free to catch and handle errors however you like. You could use an
29       "eval" block to catch Moose exceptions. However, the Moose team
30       strongly recommends using Try::Tiny instead. Please refer to
31       Try::Tiny's documentation for a discussion of how "eval" is dangerous.
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33       The following example demonstrates how to catch and inspect a
34       Moose::Exception. For the sake of simplicity, we will cause a very
35       simple error. The "extends" keywords expects a list of superclass
36       names. If we pass no superclass names, Moose will throw an instance of
37       Moose::Exception::ExtendsMissingArgs.
38
39   Catching with Try::Tiny
40           use warnings;
41           use strict;
42           use Try::Tiny;
43
44           try {
45               package Example::Exception;
46               use Moose;
47               extends;    # <-- error!
48           }
49           catch {
50               # $_ contains the instance of the exception thrown by the above try
51               # block, but $_ may get clobbered, so we should copy its value to
52               # another variable.
53               my $e = $_;
54
55               # Exception objects are not ubiquitous in Perl, so we must check
56               # whether $e is blessed. We also need to ensure that $e is actually
57               # the kind of exception we were expecting.
58               if ( blessed $e
59                   && $e->isa('Moose::Exception::ExtendsMissingArgs') ) {
60
61                   my $class_name = $e->class_name;
62                   warn "You forgot to specify a superclass for $class_name, silly!";
63               }
64
65               # It's either another type of an object or not an object at all.
66               else {
67                   warn "$e\n";
68               }
69           };
70
71   Example of catching ValidationFailedForTypeConstraint
72           use warnings;
73           use strict;
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75           use Try::Tiny;
76
77           {
78               package Person;
79               use Moose;
80               use Moose::Util::TypeConstraints;
81
82               subtype 'NameStr',
83                   as 'Str',
84                   where { $_ =~ /^[a-zA-Z]+$/; };
85
86               has age => (
87                   is       => 'ro',
88                   isa      => 'Int',
89                   required => 1
90               );
91
92               has name => (
93                   is       => 'ro',
94                   isa      => 'NameStr',
95                   required => 1
96               );
97           }
98
99           my $person;
100           while ( !$person ) {
101               try {
102                   print 'Enter your age : ';
103                   my $age = <STDIN>;
104                   chomp $age;
105                   print 'Enter your name : ';
106                   my $name = <STDIN>;
107                   chomp $name;
108                   $person = Person->new(
109                       age  => $age,
110                       name => $name
111                   );
112                   my $person_name = $person->name;
113                   my $person_age  = $person->age;
114                   print "$person_name is $person_age years old\n";
115               }
116               catch {
117                   my $e = $_;
118
119                   if (
120                       blessed $e
121                       && $e->isa(
122                           'Moose::Exception::ValidationFailedForTypeConstraint')
123                       ) {
124
125                       my $attribute_name = $e->attribute->name;
126                       my $type_name      = $e->type->name;
127                       my $value          = $e->value;
128
129                       warn
130                           "You entered $value for $attribute_name, which is not a $type_name!";
131                   }
132                   else {
133                       warn "$e\n";
134                   }
135               };
136           }
137
138   Example of catching AttributeIsRequired
139           use warnings;
140           use strict;
141           use Try::Tiny;
142
143           {
144               package Example::RequiredAttribute;
145               use Moose;
146
147               has required_attribute => (
148                   is       => 'ro',
149                   isa      => 'Int',
150                   required => 1
151               );
152           }
153
154           try {
155               # we're not passing required_attribute, so it'll throw an exception
156               my $object = Example::RequiredAttribute->new();
157           }
158           catch {
159               my $e = $_;
160               if ( blessed $e && $e->isa('Moose::Exception::AttributeIsRequired') )
161               {
162                   warn $e->message, "\n";
163               }
164               else {
165                   warn "$e\n";
166               }
167           };
168

MOOSE EXCEPTION CLASSES

170       All the exception classes are listed in
171       Moose::Manual::Exceptions::Manifest.
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AUTHORS

174       •   Stevan Little <stevan@cpan.org>
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176       •   Dave Rolsky <autarch@urth.org>
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178       •   Jesse Luehrs <doy@cpan.org>
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180       •   Shawn M Moore <sartak@cpan.org>
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182       •   יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
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184       •   Karen Etheridge <ether@cpan.org>
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186       •   Florian Ragwitz <rafl@debian.org>
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188       •   Hans Dieter Pearcey <hdp@cpan.org>
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190       •   Chris Prather <chris@prather.org>
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192       •   Matt S Trout <mstrout@cpan.org>
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195       This software is copyright (c) 2006 by Infinity Interactive, Inc.
196
197       This is free software; you can redistribute it and/or modify it under
198       the same terms as the Perl 5 programming language system itself.
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202perl v5.34.0                      2021-07-22      Moose::Manual::Exceptions(3)
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