--- name: "Badger::Base" section: "3pm" platform: "linux" package: "libbadger-perl" version: "0.16-3" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/Badger::Base" --- # Badger::Base(3pm) base class module ## NAME Badger::Base - base class module ## SYNOPSIS ``` # define a new object class derived from Badger::Base package Your::Badger::Module; use base 'Badger::Base'; sub init { my ($self, $config) = @_; # $config is a hash of named parameters # - let's assume 'name' is mandatory $self->{ name } = $config->{ name } || return $self->error('no name specified'); # save the rest of the config for later $self->{ config } = $config; # return $self to indicate success return $self; } # ...any other methods follow.... # now use it use Your::Badger::Module my $object = Your::Badger::Module->new( name => 'Brian' ); ``` ## DESCRIPTION This module implements a base class object from which most of the other `"Badger"` modules are derived. It implements a number of methods to aid in object creation, configuration, error handling and debugging. You can use it as a base class for your own modules to inherit the methods that it provides. ``` package Your::Badger::Module; use base 'Badger::Base'; ``` You can inherit the default **new()** constructor method and define your own **init()** method to initialise objects. ``` sub init { my ($self, $config) # $config is a hash of named parameters # - let's assume 'name' is mandatory $self->{ name } = $config->{ name } || return $self->error('no name specified'); # save the rest of the config in case any other # methods want to use it later $self->{ config } = $config; # return $self to indicate success return $self; } ``` You can then use your module and instantiate objects. The **new()** method accepts a list or reference to a hash array of named parameters. ``` use Your::Badger::Module; # list of named parameters my $object = Your::Badger::Module->new( name => 'Brian' ); # hash ref of name parameters my $object = Your::Badger::Module->new({ name => 'Brian' }); ``` `"Badger::Base"` provides a number of other methods that are generally suitable for all (or most) objects to inherit. These include methods for error reporting, debugging and raising warnings. ## METHODS ### new(\\%config) This is a general purpose constructor method. It accepts either a reference to a hash array of named parameters or a list of named parameters which are then folded into a hash reference. ``` # hash reference of named params my $object = Your::Badger::Module->new({ arg1 => 'value1', arg2 => 'value2', ...etc... }); # list of named params my $object = Your::Badger::Module->new( arg1 => 'value1', arg2 => 'value2', ...etc... ); ``` The constructor creates a new object by blessing a hash reference and then calling the `"init()"` method. A reference to the hash array of named parameters is passed as a single argument. In most cases you should be able to re-use the existing **new()** method and define your own **init()** method to initialise the object. The `"new()"` method returns whatever the **init()** method returns. This will normally be the `$self` object reference, but your own **init()** methods are free to return whatever they like. However, it must be a true value of some kind or the **new()** method will throw an error indicating that the **init()** method failed. ### init(\\%config) This initialisation method is called by the `"new()"` constructor method. This is the method that you'll normally want to redefine when you create a subclass of `"Badger::Base"`. The `"init()"` method is passed a reference to a hash array of named configuration parameters. The method may perform any configuration or initialisation processes and should generally return the `$self` reference to indicate success. ``` sub init { my ($self, $config) = @_; # set the 'answer' parameter or default to 42 $self->{ answer } = $config->{ answer } || 42; return $self; } ``` The `"init()"` method can return any true value which will then be sent back as the return value from **new()**. In most cases you'll want to return the `$self` object reference, but the possibility exists of returning other values instead (e.g. to implement singletons, prototypes, or some other clever object trickery). If something goes wrong in the `"init()"` method then you should call the **error()** method (or **error\_msg()**) to throw an error. ``` sub init { my ($self, $config) = @_; # set the 'answer' parameter or report error $self->{ answer } = $config->{ answer } || return $self->error('no answer supplied'); return $self; } ``` The only function of the default **init()** method in `"Badger::Base"` is to save a reference to the `$config` hash array in `"$self->{ config }"`. If you use the default **init()** method, or add an equivalent line to your own **init()** method, then you can defer inspection of the configuration parameters until later. For example, you might have a method which does something like this: ``` our $DATE_FORMAT = '%Y-%d-%b'; sub date_format { my $self = shift; return @_ ? ($self->{ date_format } = shift) # set from argument : $self->{ date_format } # get from self... ||= $self->{ config }->{ date_format } # ...or config... || $DATE_FORMAT; # ...or pkg var } ``` This allows you to use `"$self->{date_format}"` as a working copy of the value while keeping the original configuration value (if any) intact in `"$self->{config}->{date_format}"`. The above method will set the value if you pass an argument and return the current value if you don't. If no current value is defined then it defaults to the value in the config hash or the `$DATE_FORMAT` package variable. Now any other methods that require access to a date format need only call to the `"date_format()"` method to have it Do The Right Thing. The benefit here is that you don't have to waste time (and memory) in the **init()** method copying the `"date_format"` parameter from `$config` into `$self`. That doesn't mean that it's always the right thing to do, but it can be useful for configuration options that are infrequently used. The **on\_error()** and **on\_warn()** methods follow this protocol. They look for an `"ON_ERROR"` or `"ON_WARN"` item in `$self` or an `"on_error"` or `"on_warn"` parameter in `"$self->{config}"`. If you want to define `"on_error"` and/or `"on_warn"` handlers as configuration parameters then you'll need to either copy the `$config` reference into `"$self->{config}"` or copy the individual items into `"$self->{ON_ERROR}"` and/or `"$self->{ON_WARN}"`, respectively. ``` # either copy the config... sub init { my ($self, $config) = @_; $self->{ config } = $config; # ...more code... return $self; } # ...or the individual items sub init { my ($self, $config) = @_; # no need to check if either of these are defined because the # on_warn() and on_error() methods will Do The Right Thing. $self->{ ON_WARN } = $config->{ on_warn }; $self->{ ON_ERROR } = $config->{ on_error }; # ...more code... return $self; } ``` With either of the above in place, you can then define `"on_warn"` and `"on_error"` handlers and expect them to work when the **error()** and **warn()** methods are called. ``` my $object = Your::Badger::Module->new( on_warn => \&my_warn, on_error => \&my_error, ); $object->warn("Rebel Alliance engaging"); # calls my_warn() $object->error("Exhaust port unshielded!"); # calls my_error() ``` ### warn($message) A method to raise a warning. The default behaviour is to forward all arguments to Perl's `"warn"` function. However, you can install your own warning handlers on a per-class or per-object basis using the **on\_warn()** method or by setting a `$ON_WARN` package variable in your module. See **on\_warn()** for further details. ``` $object->warn("Careful with that axe, Eugene!"); ``` ### on\_warn($handler, $another\_handler, ...) This method allows you to install one or more callback handlers which are called whenever a warning is raised via the **warn()** method. Multiple handlers can be installed and will be called in turn whenever an error occurs. The warning message is passed as an argument to the handlers. For example, if you wanted to forward warning messages to your favourite logging tool, you might do something like this: ``` my $log = My::Fave::Log::Tool->new(%log_config); $object->on_warn( sub { my $message = shift; $log->warning("$message); return $message; } ); ``` The value returned from the callback is forwarded to the next handler (if there is one). If a callback returns a false value or an empty list then the remaining handlers will not be called. The default behaviour of the `"on_warn()"` method is to replace any existing warning handlers with the new one(s) specified. You can prefix the handler(s) with `'before'` or `'after'` to add them to the existing list of handlers. e.g. ``` $object->on_warn( before => \&one, \&two ); $object->on_warn( after => \&one, \&two ); ``` The **on\_warn()** method returns a reference to the list, so you can also monkey about with it directly if you want the handler(s) to go somewhere else. ``` my $handlers = $object->on_warn; shift(@$handlers, \&one); # add before existing handlers push(@$handlers, \&two); # add after existing handlers ``` You can also specify a method name as a warning handler. For example, if you want to automatically upgrade all warnings to errors for a particular object, you can write this: ``` $object->on_warn('error'); # calls $object->error() on warnings ``` You can also specify `'warn'` as a handler which will call Perl's `"warn()"` function. This is the default value. To explicitly disable any handlers, you can use a value of `0`. ``` $object->on_warn('warn'); # raise warning - the default action $object->on_warn(0); # no warnings ``` These values can be imported from Badger::Constants as the `"WARN"` and `"NONE"` constants. ``` use Badger::Constants 'WARN NONE'; $object->on_warn(WARN); # raise warning - the default action $object->on_warn(NONE); # no warnings ``` The **on\_warn()** method works equally well as a class method. In this case it sets the `$ON_WARN` package variable for the class. This acts as the default handler list for any objects of that class that don't explicitly define their own warning handlers. ``` Your::Badger::Module->on_warn(\&handler_sub); ``` If you prefer you can define this using the `$ON_WARN` package variable. This will then be used as the default for all objects of this class. ``` package Your::Badger::Module; use base 'Badger::Base'; our $ON_WARN = \&handler_sub; ``` Multiple values should be defined using a list reference. Method names and the special `"warn"` flag can also be included. ``` our $ON_WARN = [ \&this_code_first, 'this_method_next', 'warn' ] ``` ### error($message) The `"error()"` method is used for error reporting. When an object method fails for some reason, it calls the `"error()"` method passing an argument denoting the problem that occurred. This causes an exception object to be created (see Badger::Exception) and thrown via `"throw()"`. In this case the `"error()"` method will never return. ``` sub engage { my $self = shift; return $self->error('warp drive offline'); } ``` Multiple arguments can be passed to the `"error()"` method. They are concatenated into a single string. ``` sub engage { my $self = shift; return $self->error( 'warp drive ', $self->{ engine_no }, ' is offline' ); } ``` The error method can also be called without arguments to return the error message previously thrown by a call to `"error()"`. In this case it performs exactly the same function as the **reason()** method. ``` eval { $enterprise->engage } || warn "Could not engage: ", $enterprise->error; ``` The fact that the `"error()"` method can be called without arguments allows you to write things like this: ``` # doesn't throw anything if list is empty $self->error(@list_of_errors); ``` An existing exception object can also be passed as a single argument to the error method. In this case, the exception object is re-thrown unmodified. ``` sub save_the_world { eval { $self->world_peace }; if ($@) { $self->call_international_rescue($@); # call Thunderbirds return $self->error($@); # re-throw error }; } ``` ASIDE: You may have noticed in these examples that I'm using the `"return"` keyword when raising an error. For example: ``` return $self->error('warp drive offline'); ``` The `"error()"` method doesn't return when you call it with arguments so the `"return"` keyword has no effect whatsoever. However, I like to put it there to give a clear indication of what my intentions are at that point. It also means that the code will continue to return even if a subclass should "accidentally" define a different **error()** method that doesn't throw an error (don't laugh - it happens). It's also useful when used in conjunction with syntax highlighting to see at a glance where the potential exit points from a method are (assuming you make `"return"` bright red or something obvious like I do). The `"error()"` method can also be called as a class method. In this case, it updates and retrieves the `$ERROR` package variable in the package of the subclass module. This can be used to raise and examine errors thrown by class methods. ``` # calling package error() method my $object = eval { Your::Badger::Module->new() } || warn "Could not create badger module: ", Your::Badger::Module->error(); # accessing $ERROR package variable my $object = eval { Your::Badger::Module->new() } || warn 'Could not create badger module: ", $Your::Badger::Module::ERROR; ``` ### on\_error($handler, $another\_handler, ...) This method is similar to **on\_warn()** in allowing you to install a callback handler which is called whenever an error is raised via the **error()** method (or the **error\_msg()** wrapper). ``` $world->on_error( sub { my $message = shift; Thunderbirds->call({ priority => IR_PRIORITY_HIGH, message => $message, }); return $message; # forward message to next handler } ); ``` The value returned from the callback is forwarded to the next handler. If a callback returns a false value or an empty list then the remaining handlers will not be called. However, the error will still be raised regardless of what any of the handlers do or return. ### decline($reason, $more\_reasons, ...) The `"decline()"` method is used to indicate that a method failed but without raising an error. It is typically used for methods that are asked to fetch a resource (e.g. a record in a database, file in a filesystem, etc.) that may not exist. In the case where it *isn't* considered an error if the requested resource is missing then the method can call the **decline()** method. It works like **error()** in that it stores the message internally for later inspection via **reason()**. But instead of throwing the message as an exception, it simply returns `"undef"` ``` sub forage { my ($self, $name) = @_; # hard error if database isn't connected my $db = $self->{ database } || return $self->error('no database') if ($thing = $db->fetch_thing($name)) { # return true value on success return $thing; } else { # soft decline if not found return $self->decline("not found: $name") } } ``` Like **error()**, the **decline()** method can be called without arguments to return the most recent decline message, although it's probably better to use **reason()** which is designed specifically for that purpose. The **decline()** method can also be called as a class method as well as an object method, as per **error()**. ### declined() Returns the values of the internal flag which indicates if an object declined by calling the **decline()** method. This is set to `1` whenever the **decline()** method is called and cleared back to `0` whenever the **error()** method is called. ``` my $result = eval { $forager->fetch('nuts') }; if ($result) { print "result: $result\n"; } elsif ($forager->declined) { print "declined: ", $forager->reason, "\n"; } else { print "error: ", $forager->reason, "\n"; } ``` ### reason() Returns the message generated by the most recent call to **error()** or **decline()** (or any of the wrapper methods like **error\_msg()** and **decline\_msg()**). ``` $forager->forage('nuts and berries') || die $forager->reason; ``` ### message($type, @args) This method generates a message using a pre-defined format. Message formats should be defined in a `$MESSAGES` package variable in the object's package or one of its base classes. ``` # base class package Badger::Example::One use base 'Badger::Base'; our $MESSAGES = { hai => 'Hello %s', }; # subclass package Badger::Example::Two; use base 'Badger::Example::One'; our $MESSAGES = { bye => 'Goodbye %s', }; # using the classes package main; my $two = Badger::Example::Two->new(); $two->message( hai => 'World' ); # Hello World $two->message( bye => 'World' ); # Goodbye World ``` The `$two` object can use message formats defined in its own package (`"Badger::Example::Two"`) and also those of its base class (`"Badger::Example::One"`). The messages are formatted using the **xprintf()** function in Badger::Utils. This is a thin wrapper around the built-in `"sprintf()"` function with some additional formatting controls to simplify the process of using positional arguments. Messages are used internally by the **error\_msg()** and **decline\_msg()** methods for generating error messages, but you can use them for any kind of simple message generation. There are a number of benefits to defining messages in a central repository like this. First, it makes it easy to reuse the same message format in different places. Also known as the "DRY" principle - *Don't Repeat Yourself*. Second, it allows you to put all your messages in one place instead of dotting them all over your code. The benefit here is a clearer *separation of* *concerns* between the underlying logic of your application and the presentational aspects. The third benefit comes as a result of this clear separation - it becomes trivially easy to change the messages generated by your application because they're all defined in one place (possibly in several different modules if that's how you choose to break it down, but at least they're in *one* place in each of those modules). Possible applications of this include: localising an application to different spoken languages; generating messages in colour (as the Badger::Debug and Badger::Test modules do); or formatting messages as HTML. ### warn\_msg($message, @args) This is a wrapper around the **warn()** and **message()** methods. The first argument defines a message format. The remaining arguments are then applied to that format via the **message()** method. The resulting output is then forwarded to the **warn()** method. ``` our $NAME = 'Badger'; our $MESSAGES = { using_default => "Using default value for %s: %s", }; sub init { my ($self, $config) = @_; if ($config->{ name }) { $self->{ name } = $config->{ name }; } else { $self->warn_msg( using_default => name => $NAME ); $self->{ name } = $NAME; } return $self; } ``` If a `"name"` isn't provided as a configuration parameter then the default `$NAME` will be used and the following warning will be generated: ``` Using default value for name: Badger ``` ### error\_msg($message, @args) This is a wrapper around the **error()** and **message()** methods, similar to **warn\_msg()**. ``` package Your::Zoo; use base 'Badger::Base'; our $MESSAGES = { not_found => "I can't find the %s you asked for: %s", } sub animal { my ($self, $name) = @_; return $self->fetch_an_animal($name) || $self->error_msg( missing => animal => $name ); } ``` Calling the `"animal()"` method on this object with an animal that can't be found, like this: ``` $zoo->animal('Badgerpotamus'); ``` Will generate an error message like this: ``` your.zoo error - I can't find the animal you asked for: Badgerpotamus ``` ### decline\_msg($message, @args) This is a wrapper around the **decline()** and **message()** methods, similar to **warn\_msg()** and **error\_msg()**. ``` our $MESSAGES = { not_found => 'No %s found in the forest', }; sub forage { my ($self, $name) = @_; return $self->database->fetch_item($name) || $self->decline_msg( not_found => $name ); } ``` The **reason()** method can be used to return the message generated. ``` my $food = $forager->forage('nuts') || warn $forager->reason; # No nuts found in the forest ``` ### fatal\_msg($message, @args) This is a wrapper around the **fatal()** and **message()** methods, similar to **error\_msg()** and co. ### throw($type, $info, %more\_info) This method throws an exception by calling `"die()"`. It can be called with one argument, which can either be a Badger::Exception object (or subclass), or an error message which is upgraded to an exception object (which makes it behave exactly the same as **error()**). ``` # error message - same thing as error() $object->throw('an error has occurred'); # exception object $e = Badger::Exception->new( type => 'engine', info => 'warp drive offline' ); $object->throw($e); ``` In the first case, the **exception()** and **throws()** methods will be called to determine the exception class (Badger::Exception by default) and type for the exception, respectively. The method can also be called with two arguments. The first defines the exception `"type"`, the second the error message. ``` $object->throw( engine => 'warp drive offline' ); ``` The second argument can also be another exception object. If the exception has the same type as the first argument then it is re-thrown unchanged. ``` $e = Badger::Exception->new( type => 'engine', info => 'warp drive offline' ); $object->throw( engine => $e ) }; ``` In the example above, the `$e` exception already has a type of `"engine"` and so is thrown without change. If the exception types don't match, or if the exception isn't the right kind of exception object that we're expecting (as reported by **exception()**) then a new exception is thrown with the old one attached via the `"info"` field. ``` $object->throw( propulsion => $e ); ``` Here a new `"propulsion"` exception is thrown, with the previous `"engine"` exception linked in via the `"info"` field. The exception object has **type()** and **info()** methods that allow you to inspect its value, iteratively if necessary. Or you can just print an exception and rely on its overloaded stringification operator to call the **text()** method. For the error thrown in the previous example, that would be: ``` propulsion error - engine error - warp drive offline ``` ### throw\_msg($type, $message, @args) This is a wrapper around the **throw()** and **message()** methods for throwing custom exceptions using message formats to generate the error information string. The first argument defines the exception type. The second is the name of the message format. The remaining arguments are uses to populate the placeholders in the message format. ``` our $MESSAGES = { offline => '%s is offline', }; sub engage { my $self = shift; $self->throw_msg( warp => offline => 'warp drive' ) unless $self->warp_drive_ready; # make it so } # throws the following exception: warp error - warp drive is offline ``` ### try($method, @args) This method wraps another method call in an `"eval"` block to catch any exceptions thrown. ``` my $result = $object->try( fetch => 'answer' ) || 42; ``` This example is equivalent to: ``` my $result = eval { $object->fetch('answer') } || 42; ``` The error thrown can be retrieved using the `"reason()"` method. ``` my $result = $object->try( fetch => 'answer' )|| do { warn "Could not fetch answer: ", $object->reason; 42; # a sensible default }; ``` If you call the `"try()"` method without any arguments then it will return a `"Badger::Base::Trial"` object as a wafer thin wrapper around the original object. Any methods called on this delegate object will be forwarded to the original object, wrapped up in an `"eval"` block to catch any errors thrown. ``` my $result = $object->try->fetch('answer') ||= do { ... }; ``` ### catch($type, $method, @args) TODO - this method depends on some code in Badger::Exception which I haven't written yet. ### throws($type) You can set the default exception type for **throw()** by calling the **throws()** method with an argument, either as an object method (to affect that object only) or as a class method (to affect all objects that don't set their own value explicitly). Note that the **error()** and **error\_msg()** methods call **throw()** internally, so changing the exception type will also affect the exceptions thrown by those methods. ``` # object method $object->throws('food'); $object->throw('No nuts'); # food error - No nuts $object->error('No nuts'); # food error - No nuts # class method Badger::Example->throws('food'); Badger::Example->throw('No berries'); # food error - No berries Badger::Example->error('No berries'); # food error - No berries # all objects of this class now throw food by default my $badger = Badger::Example->new; $badger->throw('No cheese'); # food error - No cheese $badger->error('No cheese'); # food error - No cheese ``` You can also set this value for an object by passing a `"throws"` configuration parameter to the **new()** constructor method. ``` my $badger = Badger::Example->new( throws => 'food', ); ``` This relies on the default behaviour of the **init()** method which stores a reference to the original configuration parameters in `"$self->{config}"`. If you want to use this feature then you should ensure that any specialised **init()** method you define does the same thing, or copies the `"throws"` value from `$config` into `"$self->{THROWS}"`. ``` # example 1: store entire config for later sub init { my ($self, $config) = @_; $self->{ config } = $config; # do other stuff return $self; } # example 2: extract specific parameter up front sub init { my ($self, $config) = @_; $self->{ THROWS } = $config->{ throws }; # do other stuff return $self; } ``` You can set the default exception type for your own modules that inherit from `"Badger::Base"` by adding a `$THROWS` package variable; ``` package Badger::Example; use base 'Badger::Base'; our $THROWS = 'food'; ``` If you don't specify an exception type then one will be generated from the module's class name using the **id()** method in Badger::Class. ### exception($class) This method can be used to get or set the exception class for an object. The default value is Badger::Exception. ``` use Badger::Example; use Some::Other::Exception; Badger::Example->exception('Some::Other::Exception'); # now Badger::Example objects throw Some::Other::Exception ``` You can set the default exception class for your own modules that inherit from `"Badger::Base"` by adding a `$EXCEPTION` package variable; ``` package Badger::Example; use base 'Badger::Base'; use Some::Other::Exception; our $EXCEPTION = 'Some::Other::Exception'; ``` ### fatal($info, $more\_info, ...) This method is used internally to raise a fatal error. It bypasses the normal error reporting mechanism and dies with a stack backtrace by calling `"confess()"` (see Carp). The most common reason for a fatal error being raised is calling the **message()** method (or either of the **error\_msg()** or **decline\_msg()** wrapper methods) with a message format that doesn't exist. The stack backtrace will tell you where in your code you're making the call so you can easily find and fix it. ### not\_implemented($what) A method of convenience which raises an error indicating that the method isn't implemented ``` sub example_method { shift->not_implemented; } ``` Calling the `"example_method()"` would result in an error message similar to this (shown here split across two lines): ``` your.badger.module error - example_method() is not implemented for Your::Badger::Module in /path/to/your/script.pl at line 42 ``` Note that it tells you where the `"example_method()"` was called from, not where the method is defined. The `"not_implemented()"` method is typically used in methods defined in a base classes that subclasses are expected to re-define (a.k.a. pure virtual methods or abstract methods). You can pass an argument to be more specific about what it is that isn't implemented. ``` sub example_method { shift->not_implemented('in base class'); } ``` The argument is added to the generated error message following the method name. A single space is also added to separate them. ``` your.badger.module error - example_method() is not implemented in base class for Your::Badger::Module in ...etc... ``` ### todo($what) A method of convenience useful during developing to indicate that a method isn't implemented yet. It raises an error stating that the method is still TODO. ``` sub not_yet_working { shift->todo; } ``` The error message generated looks something like this: ``` your.badger.module error - not_yet_working() is TODO in Your::Badger::Module at line 42 ``` You can pass an argument to be more specific about what is still TODO. ``` sub not_yet_working { my ($self, $x) = @_; if (ref $x) { $self->todo('support for references'); } else { # do something } } ``` The error message generated would then be: ``` your.badger.module error - not_yet_working() support for references is TODO in Your::Badger::Module at line 42 ``` ### debug($msg1,$msg2,...) This method is mixed in from the Badger::Debug module. It provides a simple way of generating debugging messages which include the source module and line number where the message was generated. ``` sub example { my $self = shift; $self->debug('entered example()'); # ... some code ... $self->debug('leaving example()'); } ``` ### debug\_msg($message, @args) This is a wrapper around the **debug()** and **message()** methods, similar to **warn\_msg()**, **error\_msg()** and friends. ``` our $MESSAGES = { here => 'You are in %s', }; sub example { my $self = shift; $self->debug_msg( here => 'a maze of twisty little passages, all alike' ) if DEBUG; # ... some code ... $self->debug_msg( here => 'boat, floating on a sea of purest green' ) if DEBUG; } ``` ### debug\_up($level,$msg1,$msg2,...) Another debugging method mixed in from Badger::Debug. This is a wrapper around **debug()** which reports the file and line number of a caller higher up the call stack. This is typically used when you create your own debugging methods, as shown in the following example. ``` sub parse { my $self = shift; while (my ($foo, $bar) = $self->get_foo_bar) { $self->trace($foo, $bar); # report line here # do something } } sub trace { my ($self, $foo, $bar) = @_; $self->debug_up(2, "foo: $foo bar: $bar"); # not here } ``` See Badger::Debug for further details. ## PACKAGE VARIABLES The `"Badger::Base"` module uses a number of package variables to control the default behaviour of the objects derived from it. ### $DEBUG This flag can be set true to enable debugging in `"Badger::Base"`. ``` $Badger::Base::DEBUG = 1; ``` The `"Badger::Base"` module does not use or define any `$DEBUG` variable in the subclasses derived from it. However, you may want to do something similar in your own modules to assist in debugging. ``` package Your::Badger::Module; use base 'Badger::Base'; # allow flag to be set before this module is loaded our $DEBUG = 0 unless defined $DEBUG; sub gnarly_method { my ($self, $item) = @_; $self->debug("gnarly_method($item)\n") if $DEBUG; # your gnarly code } ``` The `"Badger::Class"` module defines the `"debug"` method and import hook which will automatically define a `$DEBUG` variable for you. ``` package Your::Badger::Module; use Badger::Class base => 'Badger::Base', debug => 0; ``` ### $DECLINED This package variable is defined in each subclass derived from `"Badger::Base"`. It is a boolean (0/1) flag used by the **error()**, **decline()** and **declined()** methods. The **decline()** method sets it to `1` to indicate that the object declined a request. The **error()** method clears it back to `0` to indicate that a hard error occurred. The **declined()** method simply returns the value. ### $ERROR This package variable is defined in each subclass derived from `"Badger::Base"`. It stores the most recent error message raised by **decline()** or **error()**. ### $EXCEPTION This package variable is used to define the name of the class that should be used to instantiate exception objects. The default value in `"Badger::Base"` is `"Badger::Exception"`. Subclasses may define an `$EXCEPTION` package variable to change this value. ``` package Your::Badger::Module; use base 'Badger::Base'; use Your::Exception; our $EXCEPTION = 'Your::Exception'; ``` Those that don't explicitly define an `$EXCEPTION` will inherit the value from any of their base classes, possibly coming all the way back up to the default value in `"Badger::Base"`. Calling the `"exception()"` class method with an argument will update the `$EXCEPTION` package variable in that class. ``` # sets $Your::Badger::Module::EXCEPTION Your::Badger::Module->exception('Your::Exception'); ``` ### $MESSAGES This package variable is used to reference a hash array of messages that can be used with the **message()**, **warn\_msg()**, **error\_msg()** and **decline\_msg()** methods. The `"Badger::Base"` module defines a number of messages that it uses internally. ``` our $MESSAGES = { not_found => '%s not found: %s', not_found_in => '%s not found in %s', not_implemented => '%s is not implemented %s', no_component => 'No %s component defined', bad_method => "Invalid method '%s' called on %s at %s line %s", invalid => 'Invalid %s specified: %s', unexpected => 'Invalid %s specified: %s (expected a %s)', missing_to => 'No %s specified to %s', missing => 'No %s specified', todo => '%s is TODO %s', at_line => '%s at line %s', at_file_line => '%s in %s at line %s', }; ``` The **message()** method searches for `$MESSAGES` in the current class and those of any base classes. That means that any objects derived from `"Badger::Base"` can use these message formats. ``` package Your::Badger::Module; use base 'Badger::Base'; sub init { my ($self, $config) = @_; $self->{ name } = $config->{ name } || $self->error_msg( missing => $name ); return $self; } ``` You can define additional `$MESSAGES` for your own classes. ``` package Your::Badger::Module; use base 'Badger::Base'; our $MESSAGES = { life_jim => "It's %s Jim, but not as we know it", } sub bones { my ($self, $thing)= @_; $self->warn_msg( life_jim => $thing ); return $self; } ``` Calling the `"bones()"` method like this: ``` $object->bones('a badger'); ``` will generate a warning like this: ``` It's a badger Jim, but not as we know it. ``` ### $ON\_ERROR This package variable is used to define one or more error handlers that will be invoked whenever the **error()** method is called. The `"Badger::Base"` module doesn't define any `$ON_ERROR` package variable by default. The **on\_error()** method can be called as a class method to set the `$ON_ERROR` package variable. ``` Your::Badger::Module->on_error(\&my_handler); ``` You can also define an `$ON_ERROR` handler or list of handlers in your module. ``` package Your::Badger::Module; use base 'Badger::Base'; # one of the following... our $ON_ERROR = 'warn'; # call Perl's warn() our $ON_ERROR = 'method_name'; our $ON_ERROR = \&code_ref; our $ON_ERROR = [ 'warn', 'method_name', \&code_ref ]; # code refs get message as first argument sub code_ref { my $message = shift; # do something... } # methods get implicit $self, then message argument sub method_name { my ($self, $message) = @_; # do something... } ``` ### $ON\_WARN This package variable is used to define one or more error handlers that will be invoked whenever the **warning()** method is called. It works in exactly the same way as `$ON_ERROR`. ### $THROWS This package variable is used to define the default exception type thrown by the **throw()** method (and **error()** and **error\_msg()** which call it indirectly). It can be set by calling the **throws()** class method. ``` Your::Badger::Module->throws('food'); ``` You can define `$THROWS` in your own modules that are derived from `"Badger::Base"`. ``` package Your::Badger::Module; use base 'Badger::Base'; our $THROWS = 'food'; ``` If the `$THROWS` value is not defined in the current class or any of an object's base classes, then the **id()** method is used to construct an identifier for the module to use instead. ## OBJECT INTERNALS The `"Badger::Base"` module uses the following internal object items to store information. ### config The default **init()** method stores a reference to the hash array of configuration parameters in the `"$self->{config}"` slot. If you're using the default **init()** method then your other methods can use this to lookup configuration parameters lazily. If you've defined your own **init()** method then this item won't exist unless your **init()** method adds it explicitly. ### DECLINED The value of the declined flag, as per the `$DECLINED` package variable. ### ERROR The last error raised, as per the `$ERROR` package variable. ### EXCEPTION Used to store the class name that should used to instantiate exceptions. Equivalent to the `$EXCEPTION` package variable but operating on a per-object basis. Can be inspected or modified by calling the **exception()** object method. ### ON\_ERROR An internal list of handlers to call when an error is raised. Equivalent to the `$ON_ERROR` package variable but operating on a per-object basis. Can be inspected or modified by calling the **on\_error()** object method. ### ON\_WARN An internal list of handlers to call when a warning is raised. Equivalent to the `$ON_WARN` package variable but operating on a per-object basis. Can be inspected or modified by calling the **on\_warn()** object method. ### THROWS Used to store the exception type that the object should throw. Equivalent to the `$THROWS` package variable but operating on a per-object basis. Can be inspected or modified by calling the **throws()** object method. ## AUTHOR Andy Wardley \ ## COPYRIGHT Copyright (C) 1996-2009 Andy Wardley. All Rights Reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.