NAME

Class::Value - Implements the Value Object Design Pattern

VERSION

version 1.100840

SYNOPSIS

        Class::Value::Boolean->new("Y");      # ok
        Class::Value::Boolean->new("hoge");   # fails

DESCRIPTION

This class, and other classes in its namespace, implement the Value Object Design Pattern. A value object encapsulates its value and adds semantic information. For example, an IPv4 address is not just a string of arbitrary characters. You can detect whether a given string is a well-formed IPv4 address and perform certain operations on it. Value objects provide a consistent interface to do this for all kinds of semantically-enhanced values.

METHODS
value
This is the method to use when getting or setting values. It includes the checks for well-formedness and validity. The values of $SkipChecks and $SkipNormalizations are respected.

When skipping checks, we still try to normalize the value, unless told not to by $SkipNormalizations. If we can't normalize it, that is, "normalize_value()" returns "undef", we use the value we were given. We don't try to normalize an undefined value lest some overridden "normalize_value()" method checks via "assert_defined()".

Skipping even normalization is useful if you want to purposefully set an denormalized value and later check whether "run_checks()" properly normalizes it.

If you absolutely need to set an value that will not be validated, use "set_value()" for that. The value stored by "set_value()" could be anything - a scalar, array, hash, coderef, another object etc. Specific value objects could also accept various input and decode it into the underlying components.

Consider, for example, a date value class that internally stores year, month and day components, for example using accessors generated by Class::Accessor::Complex. The public interface for the value object would still be "value()"; outside code never needs to know what's happening behind the scenes. However, outside code could call "year()", "month()" and "day()" on the value object and get at the components.

The date value class would override "set_value()" to parse the input and split it into the components. It would also override "is_well_formed_value()" and/or "is_valid_value()" to do some checking. And it would override get_value to return the components joined up into a date string. Thus, "stringify()" would continue to work as expected.

MUNGE_CONSTRUCTOR_ARGS
This is called by the constructor before setting attributes with the constructor's arguments. If the number of arguments is an odd value, it prepends the word "value". This allows you to write:

My::Class::Value->new('my_value');

instead of having to write

My::Class::Value->new(value => 'my_value');

add
This method is used as the overload handler for the "+" operation. It can be overridden in subclasses. In this base class it throws an Class::Value::Exception::UnsupportedOperation exception.

atan2
Like "add()" but affects the "atan2" operation.

bit_and
Like "add()" but affects the "&" operation.

bit_not
Like "add()" but affects the "~" operation.

bit_or
Like "add()" but affects the "|" operation.

bit_shift_left
Like "add()" but affects the "<<" operation.

bit_shift_right
Like "add()" but affects the ">>" operation.

bit_xor
Like "add()" but affects the "^" operation.

check
Takes the argument value, if given, or the object's currently set value and checks whether it is well-formed and valid.

comparable
As support for Data::Comparable, this method stringifies the value object. If no value is set, it returns the empty string.

cos
Like "add()" but affects the "cos" operation.

divide
Like "add()" but affects the "/" operation.

exp
Like "add()" but affects the "exp" operation.

get_value
Returns the value object's currently stored value.

int
Like "add()" but affects the "int" operation.

is_defined
Returns whether the currently stored value is defined. If there is no value set on the value object, it will return "undef".

is_valid
Takes the argument value, if given, or the object's currently set value and checks whether it is valid.

is_valid_normalized_value
Takes a normalized value as an argument and checks whether it is well-formed.

is_valid_value
Takes a value as an argument, normalizes it and checks whether the normalized value is valid. If normalization fails, that is, if it returns "undef", then this method will return 0. If the argument value - before normalization - is not defined, this method returns 1, because when no value has been set on the value object yet we don't want it to report an invalid value. If you need a different behaviour, subclass and override this method.

is_well_formed
Takes the argument value, if given, or the object's currently set value and checks whether it is well-formed.

is_well_formed_value
Takes an argument value and checks whether it is well-formed. In this base class, this method always returns 1.

iterate
Like "add()" but affects the "<>" operation.

log
Like "add()" but affects the "log" operation.

modulo
Like "add()" but affects the "%" operation.

multiply
Like "add()" but affects the "*" operation.

normalize
Takes an argument value and tries to normalize it. If the normalized value is different from the argument value, it sends out a notification by calling "send_notify_value_normalized()" - this will most likely be just informational. If normalization failed because "normalize_value()" returned "undef", a different notification is being sent using "send_notify_value_invalid()".

normalize_value
Takes an argument value and normalizes it. In this base class, the value is returned as is, but in subclasses you could customize this behaviour. For example, in a date-related value object you might accept various date input formats but normalize it to one specific format. Also see Class::Value::Boolean and its superclass Class::Value::Enum as an example.

This method should just normalize the value and return "undef" if it can't do so. It should not send any notifications; they are handled by "normalize()".

num_cmp
Like "add()" but affects the "<=>" operation.

power
Like "add()" but affects the "**" operation.

run_checks
Takes the argument value, if given, or the object's currently set value and checks whether it is valid and well-formed. The value object's exception container is cleared before those checks so notification delegates can store exceptions in this container.

If only one exception has been recorded and $ThrowSingleException is true then this individual exception will be thrown. Otherwise the whole exception container will be thrown.

run_checks_with_exception_container
Like "run_checks()", except that it takes as an additional first argument an exception container object. The exceptions accumulated during the checks are stored in this container. The container will not be thrown. This is useful if you have various value objects and you want to accumulate all exceptions in one big exception container.

The value object's own exception container will be modified during the checks and cleared afterwards.

send_notify_value_invalid
Calls "notify_value_invalid()" on the notification delegate.

send_notify_value_normalized
Calls "notify_value_normalized()" on the notification delegate.

send_notify_value_not_wellformed
Calls "notify_value_not_wellformed()" on the notification delegate.

set_value
Directly sets the argument value on the value object without any checks.

sin
Like "add()" but affects the "sin" operation.

skip_checks
You can tell the value object to omit all checks that would be run during "value()". If this method is given an argument value, it will set the package-global $SkipChecks. If no argument is given, it will return the current value of $SkipChecks. Note that this is not a per-object setting.

Temporarily skipping checks is useful if you want to set a series of value objects to values that might be invalid, for example when reading them from a data source such as a database or a configuration file, and later call "run_checks_with_exception_container()" on all of them.

You can use

Class::Value->skip_checks(1);

to temporarily skip checks, but you have to remember to call

Class::Value->skip_checks(0);

afterwards. An alternative way would be to bypass this method:

        {
            local $Class::Value::SkipChecks = 1;
            ...
        }

skip_normalizations
Like "skip_checks()", but it affects the normalizations that would be done during "value()".

sqrt
Like "add()" but affects the "sqrt" operation.

str_cmp
Like "add()" but affects the "cmp" operation.

stringify
Like "add()" but affects the "" operation.

subtract
Like "add()" but affects the "-" operation.

throw_single_exception
Like "skip_checks()", but affects $ThrowSingleException.

INSTALLATION

See perlmodinstall for information and options on installing Perl modules.

BUGS AND LIMITATIONS

No bugs have been reported.

Please report any bugs or feature requests through the web interface at <http://rt.cpan.org/Public/Dist/Display.html?Name=Class-Value>.

AVAILABILITY

The latest version of this module is available from the Comprehensive Perl Archive Network (CPAN). Visit <http://www.perl.com/CPAN/> to find a CPAN site near you, or see <http://search.cpan.org/dist/Class-Value/>.

The development version lives at
<http://github.com/hanekomu/Class-Value/>. Instead of sending patches, please fork this project using the standard git and github infrastructure.

AUTHOR

Marcel Gruenauer <marcel@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2004 by Marcel Gruenauer.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.