NAME
Exception::Base - Lightweight exceptions
SYNOPSIS
# Use module and create needed exceptions
use Exception::Base
'Exception::Runtime', # create new module
'Exception::System', # load existing module
'Exception::IO', => {
isa => 'Exception::System' }, # create new based on existing
'Exception::FileNotFound' => {
isa => 'Exception::IO', # create new based on previous
message => 'File not found', # override default message
has => [ 'filename' ], # define new rw attribute
stringify_attributes => [ 'message', 'filename' ],
}; # output message and filename
# eval/$@ (fastest method)
eval {
open my $file, '/etc/passwd'
or Exception::FileNotFound->throw(
message=>'Something wrong',
filename=>'/etc/passwd');
};
if ($@) {
my $e = Exception::Base->catch; # convert $@ into exception
if ($e->isa('Exception::IO')) { warn "IO problem"; }
elsif ($e->isa('Exception::Eval')) { warn "eval died"; }
elsif ($e->isa('Exception::Runtime')) { warn "some runtime was caught"; }
elsif ($e->with(value=>9)) { warn "something happened"; }
elsif ($e->with(qr/^Error/)) { warn "some error based on regex"; }
else { $e->throw; } # rethrow the exception
}
# alternative syntax for Perl 5.10
if ($@) {
given (my $e = Exception::Base->catch) {
when ('Exception::IO') { warn "IO problem"; }
when ('Exception::Eval') { warn "eval died"; }
when ('Exception::Runtime') { warn "some runtime was caught"; }
when ({value=>9}) { warn "something happened"; }
when (qr/^Error/) { warn "some error based on regex"; }
default { $e->throw; } # rethrow the exception
}
}
# try/catch (15x slower)
use Exception::Base ':all'; # import try/catch/throw
try eval {
open my $file, '/etc/passwd'
or throw 'Exception::FileNotFound' =>
message=>'Something wrong',
filename=>'/etc/passwd';
};
if (catch my $e) {
# $e is an exception object so no need to check if is blessed
if ($e->isa('Exception::IO')) { warn "IO problem"; }
elsif ($e->isa('Exception::Eval')) { warn "eval died"; }
elsif ($e->isa('Exception::Runtime')) { warn "some runtime was caught"; }
elsif ($e->with(value=>9)) { warn "something happened"; }
elsif ($e->with(qr/^Error/)) { warn "some error based on regex"; }
else { $e->throw; } # rethrow the exception
}
# $@ has to be recovered ASAP!
eval { die "this die will be caught" };
my $e = Exception::Base->catch;
eval { die "this die will be ignored" };
if ($e) {
(...)
}
# try/catch can be separated with another eval
try eval { die "this die will be caught" };
do { eval { die "this die will be ignored" } };
catch my $e; # only first die is recovered
# the exception can be thrown later
my $e = Exception::Base->new;
# (...)
$e->throw;
# try returns eval's value for scalar or array context
$v = try eval { do_something_returning_scalar(); };
@v = try [eval { do_something_returning_array(); }];
# ignore our package in stack trace
package My::Package;
use Exception::Base '+ignore_package' => __PACKAGE__;
# define new exception in separate module
package Exception::My;
use Exception::Base (__PACKAGE__) => {
has => ['myattr'],
};
# run Perl with changed verbosity for debugging purposes
$ perl -MException::Base=verbosity,4 script.pl
DESCRIPTION
This class implements a fully OO exception mechanism similar to
Exception::Class or Class::Throwable. It provides a simple interface
allowing programmers to declare exception classes. These classes can be
thrown and caught. Each uncaught exception prints full stack trace if
the default verbosity is uppered for debugging purposes.
The features of Exception::Base:
* fast implementation of the exception class
* fully OO without closures and source code filtering
* does not mess with $SIG{__DIE__} and $SIG{__WARN__}
* no external modules dependencies, requires core Perl modules only
* implements error stack, the try/catch blocks can be nested
* the default behaviour of exception class can be changed globally or
just for the thrown exception
* matching the exception by class, message or other attributes
* matching with string, regex or closure function
* creating automatically the derived exception classes ("use" interface)
* easly expendable, see Exception::System class for example
* prints just an error message or dumps full stack trace
* can propagate (rethrow) an exception
IMPORTS
use Exception::Base 'catch', 'try', 'throw';
Exports the catch, try and throw functions to the caller namespace.
use Exception::Base qw< catch try throw >;
try eval { throw 'Exception::Base'; };
if (catch my $e) { warn "$e"; }
use Exception::Base ':all';
Exports all available symbols to the caller namespace (catch, try
and throw).
use Exception::Base '*attribute*' => *value*;
Changes the default value for *attribute*. If the *attribute* name
has no special prefix, its default value is replaced with a new
*value*.
use Exception::Base verbosity => 4;
If the *attribute* name starts with "+" or "-" then the new *value*
is based on previous value:
* If the original *value* was a reference to array, the new
*value* can be included or removed from original array. Use
array reference if you need to add or remove more than one
element.
use Exception::Base
"+ignore_packages" => [ __PACKAGE__, qr/^Moose::/ ],
"-ignore_class" => "My::Good::Class";
* If the original *value* was a number, it will be incremeted or
decremented by the new *value*.
use Exception::Base "+ignore_level" => 1;
* If the original *value* was a string, the new *value* will be
included.
use Exception::Base "+message" => ": The incuded message";
use Exception::Base '*Exception*', ...;
Loads additional exception class module. If the module is not
available, creates the exception class automatically at compile
time. The newly created class will be based on Exception::Base
class.
use Exception::Base qw< Exception::Custom Exception::SomethingWrong >;
Exception::Custom->throw;
use Exception::Base '*Exception*' => { isa => *BaseException*, version
=> *version*, ... };
Loads additional exception class module. If the module's version is
lower than given parameter or the module can't be loaded, creates
the exception class automatically at compile time. The newly created
class will be based on given class and has the given $VERSION
variable.
isa The newly created class will be based on given class.
version
The class will be created only if the module's version is lower
than given parameter and will have the version given in the
argument.
has The class will contain new rw attibute (if parameter is a
string) or attributes (if parameter is a reference to array of
strings).
message
verbosity
max_arg_len
max_arg_nums
max_eval_len
*other attribute having default property*
The class will have the default property for the given
attribute.
use Exception::Base
'try', 'catch',
'Exception::IO',
'Exception::FileNotFound' => { isa => 'Exception::IO',
has => [ 'filename' ] },
'Exception::My' => { version => 0.2 },
'Exception::WithDefault' => { message => 'Default message' };
try eval { Exception::FileNotFound->throw( filename=>"/foo/bar" ); };
if (catch my $e) {
if ($e->isa('Exception::IO')) { warn "can be also FileNotFound"; }
if ($e->isa('Exception::My')) { print $e->VERSION; }
}
no Exception::Base 'catch', 'try', 'throw';
no Exception::Base ':all';
no Exception::Base;
Unexports the catch, try and throw functions from the caller
namespace.
use Exception::Base ':all', 'Exception::FileNotFound';
try eval { Exception::FileNotFound->throw; }; # ok
no Exception::Base;
try eval { Exception::FileNotFound->throw; }; # syntax error
CONSTANTS
ATTRS
Declaration of class attributes as reference to hash.
The attributes are listed as *name* => {*properties*}, where
*properties* is a list of attribute properties:
is Can be 'rw' for read-write attributes or 'ro' for read-only
attributes. The attribute is read-only and does not have an
accessor created if 'is' property is missed.
default
Optional property with the default value if the attribute value
is not defined.
The read-write attributes can be set with new constructor. Read-only
attributes and unknown attributes are ignored.
The constant have to be defined in derivered class if it brings
additional attributes.
package Exception::My;
our $VERSION = 0.01;
use base 'Exception::Base';
# Define new class attributes
use constant ATTRS => {
%{Exception::Base->ATTRS}, # base's attributes have to be first
readonly => { is=>'ro' }, # new ro attribute
readwrite => { is=>'rw', default=>'blah' }, # new rw attribute
};
package main;
use Exception::Base ':all';
try eval {
throw 'Exception::My' => readwrite=>2;
};
if (catch my $e) {
print $e->{readwrite}; # = 2
print $e->{defaults}->{readwrite}; # = "blah"
}
RE_NUM_INT
Represents regexp for numeric integer value.
ATTRIBUTES
Class attributes are implemented as values of blessed hash. The
attributes are also available as accessors methods.
message (rw, default: 'Unknown exception')
Contains the message of the exception. It is the part of the string
representing the exception object.
eval { Exception::Base->throw( message=>"Message" ); };
print $@->{message} if $@;
value (rw, default: 0)
Contains the value which represents numeric value of the exception
object in numeric context.
eval { Exception::Base->throw( value=>2 ); };
print "Error 2" if $@ == 2;
verbosity (rw, default: 2)
Contains the verbosity level of the exception object. It allows to
change the string representing the exception object. There are
following levels of verbosity:
* Empty string
1
Message
2
Message at %s line %d.
The same as the standard output of die() function. This is the
default option.
3
Class: Message at %s line %d
%c_ = %s::%s() called in package %s at %s line %d
...propagated in package %s at %s line %d.
...
The output contains full trace of error stack without first
ignore_level lines and those packages which are listed in
ignore_package and ignore_class settings.
4 The output contains full trace of error stack. In this case the
ignore_level, ignore_package and ignore_class settings are meaning
only for first line of exception's message.
If the verbosity is undef, then the default verbosity for exception
objects is used.
If the verbosity set with constructor (new or throw) is lower than
3, the full stack trace won't be collected.
If the verbosity is lower than 2, the full system data (time, pid,
tid, uid, euid, gid, egid) won't be collected.
This setting can be changed with import interface.
use Exception::Base verbosity => 4;
It can be also changed for Perl interpreter instance, i.e. for
debugging purposes.
sh$ perl -MException::Base=verbosity,4 script.pl
ignore_package (rw)
Contains the name (scalar or regexp) or names (as references array)
of packages which are ignored in error stack trace. It is useful if
some package throws an exception but this module shouldn't be listed
in stack trace.
package My::Package;
use Exception::Base;
sub my_function {
do_something() or throw Exception::Base ignore_package=>__PACKAGE__;
throw Exception::Base ignore_package => [ "My", qr/^My::Modules::/ ];
}
This setting can be changed with import interface.
use Exception::Base ignore_package => __PACKAGE__;
ignore_class (rw)
Contains the name (scalar) or names (as references array) of
packages which are base classes for ignored packages in error stack
trace. It means that some packages will be ignored even the derived
class was called.
package My::Package;
use Exception::Base;
Exception::Base->throw( ignore_class => "My::Base" );
This setting can be changed with import interface.
use Exception::Base ignore_class => "My::Base";
ignore_level (rw)
Contains the number of level on stack trace to ignore. It is useful
if some package throws an exception but this module shouldn't be
listed in stack trace. It can be used with or without
*ignore_package* attribute.
# Convert warning into exception. The signal handler ignores itself.
use Exception::Base 'Exception::My::Warning';
$SIG{__WARN__} = sub {
Exception::My::Warning->throw( message => $_[0], ignore_level => 1 );
};
time (ro)
Contains the timestamp of the thrown exception. Collected if the
verbosity on throwing exception was greater than 1.
eval { Exception::Base->throw( message=>"Message" ); };
print scalar localtime $@->{time};
pid (ro)
Contains the PID of the Perl process at time of thrown exception.
Collected if the verbosity on throwing exception was greater than 1.
eval { Exception::Base->throw( message=>"Message" ); };
kill 10, $@->{pid};
tid (ro)
Constains the tid of the thread or undef if threads are not used.
Collected if the verbosity on throwing exception was greater than 1.
uid (ro)
euid (ro)
gid (ro)
egid (ro)
Contains the real and effective uid and gid of the Perl process at
time of thrown exception. Collected if the verbosity on throwing
exception was greater than 1.
caller_stack (ro)
Contains the error stack as array of array with informations about
caller functions. The first 8 elements of the array's row are the
same as first 8 elements of the output of caller function. Further
elements are optional and are the arguments of called function.
Collected if the verbosity on throwing exception was greater than 1.
Contains only the first element of caller stack if the verbosity was
lower than 3.
eval { Exception::Base->throw( message=>"Message" ); };
($package, $filename, $line, $subroutine, $hasargs, $wantarray,
$evaltext, $is_require, @args) = $@->{caller_stack}->[0];
propagated_stack (ro)
Contains the array of array which is used for generating
"...propagated at" message. The elements of the array's row are the
same as first 3 elements of the output of caller function.
max_arg_len (rw, default: 64)
Contains the maximal length of argument for functions in backtrace
output. Zero means no limit for length.
sub a { Exception::Base->throw( max_arg_len=>5 ) }
a("123456789");
max_arg_nums (rw, default: 8)
Contains the maximal number of arguments for functions in backtrace
output. Zero means no limit for arguments.
sub a { Exception::Base->throw( max_arg_nums=>1 ) }
a(1,2,3);
max_eval_len (rw, default: 0)
Contains the maximal length of eval strings in backtrace output.
Zero means no limit for length.
eval "Exception->throw( max_eval_len=>10 )";
print "$@";
defaults
Meta-attribute contains the list of default values.
my $e = Exception::Base->new;
print defined $e->{verbosity}
? $e->{verbosity}
: $e->{defaults}->{verbosity};
default_attribute (default: 'message')
Meta-attribute contains the name of the default attribute. This
attribute will be set for one argument throw method. This attribute
has meaning for derived classes.
use Exception::Base 'Exception::My' => {
has => 'myattr',
default_attribute => 'myattr',
};
eval { Exception::My->throw("string") };
print $@->myattr; # "string"
numeric_attribute (default: 'value')
Meta-attribute contains the name of the attribute which contains
numeric value of exception object. This attribute will be used for
representing exception in numeric context.
use Exception::Base 'Exception::My' => {
has => 'myattr',
numeric_attribute => 'myattr',
};
eval { Exception::My->throw(myattr=>123) };
print 0 + $@; # 123
eval_attribute (default: 'message')
Meta-attribute contains the name of the attribute which is filled if
error stack is empty. This attribute will contain value of $@
variable. This attribute has meaning for derived classes.
use Exception::Base 'Exception::My' => {
has => 'myattr',
eval_attribute => 'myattr'
};
eval { die "string" };
print $@->myattr; # "string"
stringify_attributes (default: ['message'])
Meta-attribute contains the array of names of attributes with
defined value which are joined to the string returned by stringify
method. If none of attributes are defined, the string is created
from the first default value of attributes listed in the opposite
order.
use Exception::Base 'Exception::My' => {
has => 'myattr',
myattr => 'default',
stringify_attributes => ['message', 'myattr'],
};
eval { Exception::My->throw( message=>"string", myattr=>"foo" ) };
print $@->myattr; # "string: foo"
eval { Exception::My->throw() };
print $@->myattr; # "default"
OVERLOADS
Boolean context
True value.
eval { Exception::Base->throw( message=>"Message", value=>123 ) };
if ($@) {
# the exception object is always true
}
Numeric context
Content of attribute pointed by numeric_attribute attribute. See
numerify method.
eval { Exception::Base->throw( message=>"Message", value=>123 ) };
print 0+$@; # 123
String context
Content of attribute which is combined from stringify_attributes
attributes with additional informations, depended on verbosity
setting. See stringify method.
eval { Exception::Base->throw( message=>"Message", value=>123 ) };
print "$@"; # "Message at -e line 1.\n"
"~~"
Smart matching operator. See matches method.
eval { Exception::Base->throw( message=>"Message", value=>123 ) };
print $@ ~~ "Message"; # 1
print $@ ~~ qr/message/i; # 1
print $@ ~~ ['Exception::Base']; # 1
print $@ ~~ 123; # 1
print $@ ~~ {message=>"Message", value=>123}; # 1
CONSTRUCTORS
new([%*args*])
Creates the exception object, which can be thrown later. The system
data attributes like time, pid, uid, gid, euid, egid are not filled.
If the key of the argument is read-write attribute, this attribute
will be filled. Otherwise, the argument will be ignored.
$e = Exception::Base->new(
message=>"Houston, we have a problem",
unknown_attr => "BIG"
);
print $e->{message};
The constructor reads the list of class attributes from ATTRS
constant function and stores it in the internal cache for
performance reason. The defaults values for the class are also
stored in internal cache.
throw([%*args*]])
Creates the exception object and immediately throws it with die
system function.
open FILE, $file
or Exception::Base->throw( message=>"Can not open file: $file" );
The throw is also exported as a function.
open FILE, $file
or throw 'Exception::Base' => message=>"Can not open file: $file";
The throw can be also used as a method.
METHODS
throw([%*args*])
Immediately throws exception object. It can be used for rethrowing
existing exception object. Additional arguments will override the
attributes in existing exception object.
$e = Exception::Base->new;
# (...)
$e->throw( message=>"thrown exception with overriden message" );
eval { Exception::Base->throw( message=>"Problem", value=>1 ) };
$@->throw if $@->{value};
throw(*message*, [%*args*])
If the number of *args* list for arguments is odd, the first
argument is a message. This message can be overriden by message from
*args* list.
Exception::Base->throw( "Problem", message=>"More important" );
eval { die "Bum!" };
Exception::Base->throw( $@, message=>"New message" );
*CLASS*->throw($*exception*, [%*args*])
Immediately rethrows an existing exception object as an other
exception class.
eval { open $f, "w", "/etc/passwd" or Exception::System->throw };
# convert Exception::System into Exception::Base
Exception::Base->throw($@);
stringify([$*verbosity*[, $*message*]])
Returns the string representation of exception object. It is called
automatically if the exception object is used in string scalar
context. The method can be used explicity and then the verbosity
level can be used.
eval { Exception::Base->throw; };
$@->{verbosity} = 1;
print "$@";
print $@->stringify(4) if $VERY_VERBOSE;
It also replaces any message stored in object with the *message*
argument if it exists. If message argument is an empty string, the
default message is used.
eval { Exception::Base->throw( "Message" ); };
print $@->stringify(1); # "Message"
print $@->stringify(1, "Overrided"); # "Overrided"
print $@->stringify(1, ""); # "Unknown exception"
numerify
Returns the numeric representation of exception object. It is called
automatically if the exception object is used in numeric scalar
context. The method can be used explicity.
eval { Exception::Base->throw( value => 42 ); };
print 0+$@; # 42
print $@->numerify; # 42
matches(*that*)
Checks if the exception object matches the given argument. It is
somewhat similar to the with method but it takes only one argument.
The matches method overloads ~~ smart matching operator, so it can
be used with given keyword.
given ($e = Exception::Base->new( message=>"Message", value=>123 )) {
when( "Message" ) { ... } # matches
when( qr/message/i ) { ... } # matches
when( ["Exception::Base"] ) { ... } # matches
when( ["Exception::Foo", "Exception::Bar"] ) { ... } # doesn't
when( { message=>"Message" } ) { ... } # matches
when( { value=>123 } ) { ... } # matches
when( { message=>"Message", value=>45 } ) { ... } # doesn't
when( { uid=>0 } ) { ... } # matches if runs with root privileges
}
If the argument is a reference to array, it is checked if the object
is a given class.
use Exception::Base
'Exception::Simple',
'Exception::Complex' => { isa => 'Exception::Simple };
eval { Exception::Complex->throw() };
print $@ ~~ ['Exception::Base']; # matches
print $@ ~~ ['Exception::Simple', 'Exception::Other']; # matches
print $@ ~~ ['NullObject']; # doesn't
If the argument is a reference to hash, attributes of the exception
object is matched.
eval { Exception::Base->throw( message=>"Message", value=>123 ) };
print $@ ~~ { message=>"Message" }; # matches
print $@ ~~ { value=>123 }; # matches
print $@ ~~ { message=>"Message", value=>45 }; # doesn't
If the argument is a single string, regexp or code reference or is
undefined, the default attribute of the exception object is matched
(usually it is a "message" attribute).
eval { Exception::Base->throw( message=>"Message" ) };
print $@ ~~ "Message"; # matches
print $@ ~~ qr/Message/; # matches
print $@ ~~ qr/[0-9]/; # doesn't
print $@ ~~ sub{/Message/}; # matches
print $@ ~~ sub{0}; # doesn't
print $@ ~~ undef; # doesn't
If argument is a numeric value, the argument matches if value
attribute matches.
eval { Exception::Base->throw( value=>123, message=>456 ) };
print $@ ~~ 123; # matches
print $@ ~~ 456; # doesn't
with(*condition*)
Checks if the exception object matches the given condition. If the
first argument is single value, the message combined from
stringify_attributes attributes is matched. If the argument is a
part of hash, an attribute of the exception object is matched. The
with method returns true value if all its arguments match.
eval { Exception::Base->new( message=>"Message", value=>123 ) };
print $@->with( "Message" ); # matches
print $@->with( value=>123 ); # matches
print $@->with( "Message", value=>45 ); # doesn't
print $@->with( uid=>0 ); # matches if root
print $@->with( message=>"Message" ); # matches
The argument (for message or attributes) can be simple string or
code reference or regexp.
eval { Exception::Base->new( message=>"Message" ) };
print $@->with( "Message" ); # matches
print $@->with( sub {/Message/} ); # matches
print $@->with( qr/Message/ ); # matches
If argument is a numeric value, the argument matches if attribute
pointed by numeric_attribute attribute matches.
eval { Exception::Base->new( value=>123, message=>456 ) };
print $@->with( 123 ); # matches
print $@->with( 456 ); # doesn't
If argument is a reference to array, the argument matches if any of
its element matches.
eval { Exception::Base->new( message=>"Message", value=>123 ) };
print $@->with( message=>["Not", 123, 45, "Message"] ); # matches
print $@->with( value=>[123, 45], message=>"Not" ); # doesn't
The with method matches for special keywords:
-isa
Matches if the object is a given class.
eval { Exception::Base->new( message=>"Message" ) };
print $@->with( -isa=>"Exception::Base" ); # matches
print $@->with( -isa=>["Some::Class", "Exception::Base"] ); # matches
-has
Matches if the object has a given attribute.
eval { Exception::Base->new( message=>"Message" ) };
print $@->with( -has=>"Message" ); # matches
-default
Matches against the default attribute, usually the message
attribute.
eval { Exception::Base->new( message=>"Message" ) };
print $@->with( -default=>"Message" ); # matches
try(*eval*)
The try method or function can be used with eval block as argument
and then the eval's error is pushed into error stack and can be used
with catch later. The $@ variable is replaced with empty string.
try eval { Exception::Base->throw; };
eval { die "another error messing with \$@ variable"; };
catch my $e;
The try returns the value of the argument in scalar context. If the
argument is array reference, the try returns the value of the
argument in array context.
$v = Exception::Base->try( eval { 2 + 2; } ); # $v == 4
@v = Exception::Base->try( [ eval { (1,2,3); }; ] ); # @v = (1,2,3)
The try can be used as method or function.
try 'Exception::Base' => eval {
Exception::Base->throw( message=>"method" );
};
Exception::Base::try eval {
Exception::Base->throw( message=>"function" );
};
Exception::Base->import( 'try' );
try eval {
Exception::Base->throw( message=>"imported function" );
};
*CLASS*->catch([$*variable*])
The exception is popped from error stack and returned from method or
written into the method argument.
eval { Exception::Base->throw; };
if ($@) {
my $e = Exception::Base->catch;
print $e->stringify(1);
}
If the error stack is empty, the catch method recovers $@ variable
and replaces it with empty string to avoid endless loop. It allows
to use catch method without previous try.
If the popped value is not empty and does not contain the
Exception::Base object, new exception object is created with class
*CLASS* and its message is based on previous value with removed " at
file line 123." string and the last end of line (LF).
eval { die "Died\n"; };
my $e = Exception::Base->catch;
print ref $e; # "Exception::Base"
The method returns 1, if the exception object is caught, and returns
0 otherwise.
try eval { throw 'Exception::Base'; };
if (catch my $e) {
warn "Exception caught: " . ref $e;
}
If the method argument is missing, the method returns the exception
object.
eval { Exception::Base->throw; };
my $e = Exception::Base->catch;
The catch can be used as method or function. If it is used as
function, then the *CLASS* is Exception::Base by default.
try eval { throw 'Exception::Base' => message=>"method"; };
Exception::Base->import( 'catch' );
catch my $e; # the same as Exception::Base->catch( my $e );
print $e->stringify;
PROPAGATE
Checks the caller stack and fills the propagated_stack attribute. It
is usually used if die system function was called without any
arguments.
package
Returns the package name of the subroutine which thrown an
exception.
file
Returns the file name of the subroutine which thrown an exception.
line
Returns the line number for file of the subroutine which thrown an
exception.
subroutine
Returns the subroutine name which thrown an exception.
PRIVATE METHODS
_collect_system_data
Collects system data and fills the attributes of exception object.
This method is called automatically if exception if thrown. It can
be used by derived class.
package Exception::Special;
use base 'Exception::Base';
use constant ATTRS => {
%{Exception::Base->ATTRS},
'special' => { is => 'ro' },
};
sub _collect_system_data {
my $self = shift;
$self->SUPER::_collect_system_data(@_);
$self->{special} = get_special_value();
return $self;
}
__PACKAGE__->_make_accessors;
1;
Method returns the reference to the self object.
_make_accessors
Creates accessors for each attribute. This static method should be
called in each derived class which defines new attributes.
package Exception::My;
# (...)
__PACKAGE__->_make_accessors;
__stringify
Method called by overload's q{""} operator. It have to be
reimplemented in derived class if it has stringify method
implemented.
__numerify
Method called by overload's 0+ operator. It have to be reimplemented
in derived class if it has numerify method implemented.
SEE ALSO
There are more implementation of exception objects available on CPAN.
Please note that Perl has built-in implementation of pseudo-exceptions:
eval { die { message => "Pseudo-exception", package => __PACKAGE__,
file => __FILE__, line => __LINE__ };
};
if ($@) {
print $@->{message}, " at ", $@->{file}, " in line ", $@->{line}, ".\n";
}
The more complex implementation of exception mechanism provides more
features.
Error
Complete implementation of try/catch/finally/otherwise mechanism.
Uses nested closures with a lot of syntactic sugar. It is slightly
faster than Exception::Base module for failure scenario and is much
slower for success scenario. It doesn't provide a simple way to
create user defined exceptions. It doesn't collect system data and
stack trace on error.
Exception::Class
More perl-ish way to do OO exceptions. It is too heavy and too slow
for failure scenario and slightly slower for success scenario. It
requires non-core perl modules to work.
Exception::Class::TryCatch
Additional try/catch mechanism for Exception::Class. It is also slow
as Exception::Base with try/catch mechanism for success scenario.
Class::Throwable
Elegant OO exceptions without try/catch mechanism. It might be
missing some features found in Exception::Base and Exception::Class.
Exceptions
Not recommended. Abadoned. Modifies %SIG handlers.
The Exception::Base does not depend on other modules like
Exception::Class and it is more powerful than Class::Throwable. Also it
does not use closures as Error and does not polute namespace as
Exception::Class::TryCatch. It is also much faster than Exception::Class
and Error.
The Exception::Base is also a base class for enchanced classes:
Exception::System
The exception class for system or library calls which modifies $!
variable.
Exception::Died
The exception class for eval blocks with simple "die" in perlfunc.
It can also handle $SIG{__DIE__} hook and convert simple "die" in
perlfunc into an exception object.
Exception::Warning
The exception class which handle $SIG{__WARN__} hook and convert
simple "warn" in perlfunc into an exception object.
EXAMPLES
New exception classes
The Exception::Base module allows to create new exception classes easly.
You can use import interface or base module to do it.
The import interface allows to create new class with new read-write
attributes.
package Exception::Simple;
use Exception::Base (__PACKAGE__) => {
has => qw< reason method >,
stringify_attributes => qw< message reason method >,
};
For more complex exceptions you can redefine ATTRS constant.
package Exception::Complex;
use base 'Exception::Base';
use constant ATTRS => {
%{ Exception::Base->ATTRS }, # SUPER::ATTRS
hostname => { is => 'ro' },
stringify_attributes => qw< hostname message >,
};
sub _collect_system_data {
my $self = shift;
my $hostname = `hostname`;
chomp $hostname;
$self->{hostname} = $hostname;
return $self->SUPER::_collect_system_data(@_);
}
PERFORMANCE
There are two scenarios for "eval" block: success or failure. Success
scenario should have no penalty on speed. Failure scenario is usually
more complex to handle and can be significally slower.
Any other code than simple "if ($@)" is really slow and shouldn't be
used if speed is important. It means that Error and
Exception::Class::TryCatch should be avoided as far as they are slow by
design. The Exception::Class module doesn't use "if ($@)" syntax in its
documentation so it was benchmarked with its default syntax, however it
might be possible to convert it to simple "if ($@)".
The Exception::Base module was benchmarked with other implementations
for simple try/catch scenario. The results (Perl 5.10
i686-linux-thread-multi) are following:
-----------------------------------------------------------------------
| Module | Success | Failure |
-----------------------------------------------------------------------
| eval/die string | 818638/s | 237975/s |
-----------------------------------------------------------------------
| eval/die object | 849686/s | 124853/s |
-----------------------------------------------------------------------
| Exception::Base eval/if | 848593/s | 8356/s |
-----------------------------------------------------------------------
| Exception::Base try/catch | 56639/s | 9218/s |
-----------------------------------------------------------------------
| Exception::Base eval/if verbosity=1 | 849180/s | 14899/s |
-----------------------------------------------------------------------
| Exception::Base try/catch verbos.=1 | 56986/s | 18232/s |
-----------------------------------------------------------------------
| Error | 88123/s | 19782/s |
-----------------------------------------------------------------------
| Class::Throwable | 844204/s | 7545/s |
-----------------------------------------------------------------------
| Exception::Class | 344124/s | 1311/s |
-----------------------------------------------------------------------
| Exception::Class::TryCatch | 223822/s | 1270/s |
-----------------------------------------------------------------------
The Exception::Base module was written to be as fast as it is possible.
It does not use internally i.e. accessor functions which are slower
about 6 times than standard variables. It is slower than pure die/eval
because it is uses OO mechanisms which are slow in Perl. It can be a
litte faster if some features are disables, i.e. the stack trace and
higher verbosity.
You can find the benchmark script in this package distribution.
BUGS
If you find the bug, please report it.
AUTHOR
Piotr Roszatycki <
[email protected]>
LICENSE
Copyright (C) 2007, 2008 by Piotr Roszatycki <
[email protected]>.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
See <
http://www.perl.com/perl/misc/Artistic.html>
