Moose::Manual::ExceptiUser3Contributed Perl DocuMoose::Manual::Exceptions(3pm)
NAME
Moose::Manual::Exceptions - Moose's exceptions
VERSION
version 2.2203
EXCEPTIONS IN MOOSE
Moose will throw an exception for all error conditions. This applies
both to code in the Moose core as well as to all code generated when a
class is made immutable. All exceptions are subclasses of the
"Moose::Exception" class.
Each type of error has its own unique subclass, and many subclasses
have additional attributes to provide more information about the
error's context, such as what classes or roles were involved.
EXCEPTION STRINGIFICATION
By default, Moose exceptions remove Moose internals from the stack
trace. If you set the "MOOSE_FULL_EXCEPTION" environment variable to a
true value, then the Moose internals will be included in the trace.
HANDLING MOOSE EXCEPTIONS
Because Moose's exceptions use the standard "die" mechanism, you are
free to catch and handle errors however you like. You could use an
"eval" block to catch Moose exceptions. However, the Moose team
strongly recommends using Try::Tiny instead. Please refer to
Try::Tiny's documentation for a discussion of how "eval" is dangerous.
The following example demonstrates how to catch and inspect a
Moose::Exception. For the sake of simplicity, we will cause a very
simple error. The "extends" keywords expects a list of superclass
names. If we pass no superclass names, Moose will throw an instance of
Moose::Exception::ExtendsMissingArgs.
Catching with Try::Tiny
use warnings;
use strict;
use Try::Tiny;
try {
package Example::Exception;
use Moose;
extends; # <-- error!
}
catch {
# $_ contains the instance of the exception thrown by the above try
# block, but $_ may get clobbered, so we should copy its value to
# another variable.
my $e = $_;
# Exception objects are not ubiquitous in Perl, so we must check
# whether $e is blessed. We also need to ensure that $e is actually
# the kind of exception we were expecting.
if ( blessed $e
&& $e->isa('Moose::Exception::ExtendsMissingArgs') ) {
my $class_name = $e->class_name;
warn "You forgot to specify a superclass for $class_name, silly!";
}
# It's either another type of an object or not an object at all.
else {
warn "$e\n";
}
};
Example of catching ValidationFailedForTypeConstraint
use warnings;
use strict;
use Try::Tiny;
{
package Person;
use Moose;
use Moose::Util::TypeConstraints;
subtype 'NameStr',
as 'Str',
where { $_ =~ /^[a-zA-Z]+$/; };
has age => (
is => 'ro',
isa => 'Int',
required => 1
);
has name => (
is => 'ro',
isa => 'NameStr',
required => 1
);
}
my $person;
while ( !$person ) {
try {
print 'Enter your age : ';
my $age = <STDIN>;
chomp $age;
print 'Enter your name : ';
my $name = <STDIN>;
chomp $name;
$person = Person->new(
age => $age,
name => $name
);
my $person_name = $person->name;
my $person_age = $person->age;
print "$person_name is $person_age years old\n";
}
catch {
my $e = $_;
if (
blessed $e
&& $e->isa(
'Moose::Exception::ValidationFailedForTypeConstraint')
) {
my $attribute_name = $e->attribute->name;
my $type_name = $e->type->name;
my $value = $e->value;
warn
"You entered $value for $attribute_name, which is not a $type_name!";
}
else {
warn "$e\n";
}
};
}
Example of catching AttributeIsRequired
use warnings;
use strict;
use Try::Tiny;
{
package Example::RequiredAttribute;
use Moose;
has required_attribute => (
is => 'ro',
isa => 'Int',
required => 1
);
}
try {
# we're not passing required_attribute, so it'll throw an exception
my $object = Example::RequiredAttribute->new();
}
catch {
my $e = $_;
if ( blessed $e && $e->isa('Moose::Exception::AttributeIsRequired') )
{
warn $e->message, "\n";
}
else {
warn "$e\n";
}
};
MOOSE EXCEPTION CLASSES
All the exception classes are listed in
Moose::Manual::Exceptions::Manifest.
AUTHORS
• Stevan Little <stevan@cpan.org>
• Dave Rolsky <autarch@urth.org>
• Jesse Luehrs <doy@cpan.org>
• Shawn M Moore <sartak@cpan.org>
• יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
• Karen Etheridge <ether@cpan.org>
• Florian Ragwitz <rafl@debian.org>
• Hans Dieter Pearcey <hdp@cpan.org>
• Chris Prather <chris@prather.org>
• Matt S Trout <mstrout@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2006 by Infinity Interactive, Inc.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
perl v5.36.0 2023-01-30 Moose::Manual::Exceptions(3pm)
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