oracular (3) Config::Model::Value.3pm.gz

Provided by: libconfig-model-perl_2.154-1_all bug

NAME

       Config::Model::Value - Strongly typed configuration value

VERSION

       version 2.154

SYNOPSIS

        use Config::Model;

        # define configuration tree object
        my $model = Config::Model->new;
        $model ->create_config_class (
           name => "MyClass",

           element => [

               [qw/foo bar/] => {
                   type           => 'leaf',
                   value_type => 'string',
                   description => 'foobar',
               }
               ,
               country => {
                   type =>               'leaf',
                   value_type => 'enum',
                   choice =>      [qw/France US/],
                   description => 'big countries',
               }
           ,
           ],
        ) ;

        my $inst = $model->instance(root_class_name => 'MyClass' );

        my $root = $inst->config_root ;

        # put data
        $root->load( steps => 'foo=FOO country=US' );

        print $root->report ;
        #  foo = FOO
        #                DESCRIPTION: foobar
        #
        #  country = US
        #                DESCRIPTION: big countries

DESCRIPTION

       This class provides a way to specify configuration value with the following properties:

       •   Strongly typed scalar: the value can either be an enumerated type, a boolean, a number, an integer or
           a string

       •   default parameter: a value can have a default value specified during the construction. This default
           value is written in the target configuration file. ("default" parameter)

       •   upstream default parameter: specifies a default value that is used by the application when no
           information is provided in the configuration file. This upstream_default value is not written in the
           configuration files. Only the "fetch_standard" method returns the builtin value. This parameter was
           previously referred as "built_in" value. This may be used for audit purpose. ("upstream_default"
           parameter)

       •   mandatory value: reading a mandatory value raises an exception if the value is not specified (i.e is
           "undef" or empty string) and has no default value.

       •   dynamic change of property: A slave value can be registered to another master value so that the
           properties of the slave value can change according to the value of the master value. For instance,
           paper size value can be 'letter' for country 'US' and 'A4' for country 'France'.

       •   A reference to the Id of a hash of list element. In other word, the value is an enumerated type where
           the possible values (choice) is defined by the existing keys of a has element somewhere in the tree.
           See "Value Reference".

Default values

       There are several kind of default values. They depend on where these values are defined (or found).

       From the lowest default level to the "highest":

       •   "upstream_default": The value is known in the application, but is not written in the configuration
           file.

       •   "layered": The value is known by the application through another mean (e.g. an included configuration
           file), but is not written in the configuration file.

       •   "default": The value is known by the model, but not by the application. This value must be written in
           the configuration file.

       •   "computed": The value is computed from other configuration elements. This value must be written in
           the configuration file.

       •   "preset": The value is not known by the model or by the application. But it can be found by an
           automatic program and stored while the configuration Config::Model::Instance is in preset mode

       Then there is the value entered by the user. This overrides all kind of "default" value.

       The fetch_standard function returns the "highest" level of default value, but does not return a custom
       value, i.e. a value entered by the user.

Constructor

       Value object should not be created directly.

Value model declaration

       A leaf element must be declared with the following parameters:

       value_type
           Either "boolean", "enum", "integer", "number", "uniline", "string", "file", "dir". Mandatory. See
           "Value types".

       default
           Specify the default value (optional)

       upstream_default
           Specify a built in default value (optional). I.e a value known by the application which does not need
           to be written in the configuration file.

       write_as
           Array ref. Reserved for boolean value. Specify how to write a boolean value.  Default is "[0,1]"
           which may not be the most readable. "write_as" can be specified as "['false','true']" or
           "['no','yes']".

       compute
           Computes a value according to a formula and other values. By default a computed value cannot be set.
           See Config::Model::ValueComputer for computed value declaration.

       migrate_from
           This is a special parameter to cater for smooth configuration upgrade. This parameter can be used to
           copy the value of a deprecated parameter to its replacement. See "Upgrade" for details.

       convert => [uc | lc ]
           When stored, the value is converted to uppercase (uc) or lowercase (lc).

       min Specify the minimum value (optional, only for integer, number)

       max Specify the maximum value (optional, only for integer, number)

       mandatory
           Set to 1 if the configuration value must be set by the configuration user (default: 0)

       choice
           Array ref of the possible value of an enum. Example :

            choice => [ qw/foo bar/]

       match
           Perl regular expression. The value is matched with the regex to assert its validity. Example "match
           => '^foo'" means that the parameter value must begin with "foo". Valid only for "string" or "uniline"
           values.

       warn_if_match
           Hash ref. Keys are made of Perl regular expression. The value can specify a warning message (leave
           empty or undefined for a default warning message) and instructions to fix the value. A warning is
           issued when the value matches the passed regular expression. Valid only for "string" or "uniline"
           values. The fix instructions is evaluated when apply_fixes is called. $_ contains the value to fix.
           $_ is stored as the new value once the instructions are done.  $self contains the value object. Use
           with care.

           In the example below, any value matching 'foo' is converted in uppercase:

            warn_if_match => {
              'foo' => {
                   fix => 'uc;',
                   msg =>  'value $_ contains foo'
              },
              'BAR' => {
                   fix =>'lc;',
                   msg =>  'value $_ contains BAR'
              }
            },

           The tests are done in alphabetical order. In the example above, "BAR" test is done before "foo" test.

           $_ is substituted with the bad value when the message is generated. $std_value is substituted with
           the standard value (i.e the preset, computed or default value).

       warn_unless_match
           Hash ref like above. A warning is issued when the value does not match the passed regular expression.
           Valid only for "string" or "uniline" values.

       warn
           String. Issue a warning to user with the specified string any time a value is set or read.

       warn_if
           A bit like "warn_if_match". The hash key is not a regexp but a label to help users. The hash ref
           contains some Perl code that is evaluated to perform the test. A warning is issued if the given code
           returns true.

           $_ contains the value to check. $self contains the "Config::Model::Value" object (use with care).

           The example below warns if value contains a number:

            warn_if => {
               warn_test => {
                   code => 'defined $_ && /\d/;',
                   msg  => 'value $_ should not have numbers',
                   fix  => 's/\d//g;'
               }
            },

           Hash key is used in warning message when "msg" is not set:

            warn_if => {
              'should begin with foo' => {
                   code => 'defined && /^foo/'
              }
            }

           Any operation or check on file must be done with "file" sub (otherwise tests will break). This sub
           returns a Path::Tiny object that can be used to perform checks. For instance:

             warn_if => {
                warn_test => {
                    code => 'not file($_)->exists',
                    msg  => 'file $_ should exist'
                }

       warn_unless
           Like "warn_if", but issue a warning when the given "code" returns false.

           The example below warns unless the value points to an existing directory:

            warn_unless => {
                'missing dir' => {
                     code => '-d',
                     fix => "system(mkdir $_);" }
            }

       assert
           Like "warn_if". Except that returned value triggers an error when the given code returns false:

            assert => {
               test_nb => {
                   code => 'defined $_ && /\d/;',
                   msg  => 'should not have numbers',
                   fix  => 's/\d//g;'
               }
            },

           hash key can also be used to generate error message when "msg" parameter is not set.

       grammar
           Setup a Parse::RecDescent grammar to perform validation.

           If the grammar does not start with a "check" rule (i.e does not start with "check: "), the first line
           of the grammar is modified to add "check" rule and this rules is set up so the entire value must
           match the passed grammar.

           I.e. the grammar:

            token (oper token)(s?)
            oper: 'and' | 'or'
            token: 'Apache' | 'CC-BY' | 'Perl'

           is changed to

            check: token (oper token)(s?) /^\Z/ {$return = 1;}
            oper: 'and' | 'or'
            token: 'Apache' | 'CC-BY' | 'Perl'

           The rule is called with Value object and a string reference. So, in the actions you may need to
           define, you can call the value object as $arg[0], store error message in "${$arg[1]}}" and store
           warnings in "${$arg[2]}}".

       replace
           Hash ref. Used for enum to substitute one value with another. This parameter must be used to enable
           user to upgrade a configuration with obsolete values. For instance, if the value "foo" is obsolete
           and replaced by "foo_better", you must declare:

            replace => { foo => 'foo_better' }

           The hash key can also be a regular expression for wider range replacement.  The regexp must match the
           whole value:

            replace => ( 'foo.*' => 'better_foo' }

           In this case, a value is replaced by "better_foo" when the "/^foo.*$/" regexp matches.

       replace_follow
           Path specifying a hash of value element in the configuration tree. The hash if used in a way similar
           to the "replace" parameter. In this case, the replacement is not coded in the model but specified by
           the configuration.

       refer_to
           Specify a path to an id element used as a reference. See Value Reference for details.

       computed_refer_to
           Specify a path to an id element used as a computed reference. See "Value Reference" for details.

       warp
           See section below: "Warp: dynamic value configuration".

       help
           You may provide detailed description on possible values with a hash ref. Example:

           help => { oui => "French for 'yes'", non => "French for 'no'"}

           The key of help is used as a regular expression to find the help text applicable to a value. These
           regexp are tried from the longest to the shortest and are matched from the beginning of the string.
           The key "".""  or "".*"" are fallback used last.

           For instance:

            help => {
              'foobar' => 'help for values matching /^foobar/',
              'foo' => 'help for values matching /^foo/ but not /^foobar/ (used above)',
              '.' => 'help for all other values'
            }

   Value types
       This modules can check several value types:

       "boolean"
           Accepts values 1 or 0, "yes" or "no", "true" or "false", and empty string. The value read back is
           always 1 or 0.

       "enum"
           Enum choices must be specified by the "choice" parameter.

       "integer"
           Enable positive or negative integer

       "number"
           The value can be a decimal number

       "uniline"
           A one line string. I.e without "\n" in it.

       "string"
           Actually, no check is performed with this type.

       "reference"
           Like an "enum" where the possible values (aka choice) is defined by another location if the
           configuration tree. See "Value Reference".

       "file"
           A file name or path. A warning is issued if the file does not exists (or is a directory)

       "dir"
           A directory name or path. A warning is issued if the directory does not exists (or is a plain file)

Warp: dynamic value configuration

       The Warp functionality enable a "Value" object to change its properties (i.e. default value or its type)
       dynamically according to the value of another "Value" object locate elsewhere in the configuration tree.
       (See Config::Model::Warper for an explanation on warp mechanism).

       For instance if you declare 2 "Value" element this way:

        $model ->create_config_class (
            name => "TV_config_class",
            element => [
                country => {
                    type => 'leaf',
                    value_type => 'enum',
                    choice => [qw/US Europe Japan/]
                } ,
                tv_standard => { # this example is getting old...
                    type => 'leaf',
                    value_type => 'enum',
                    choice => [ qw/PAL NTSC SECAM/ ]
                    warp => {
                        follow => {
                            # this points to the warp master
                            c => '- country'
                        },
                        rules => {
                            '$c eq "US"' => {
                                 default => 'NTSC'
                             },
                            '$c eq "France"' => {
                                 default => 'SECAM'
                             },
                            '$c eq "Japan"' => {
                                 default => 'NTSC'
                             },
                            '$c eq "Europe"' => {
                                 default => 'PAL'
                            },
                        }
                    }
                } ,
            ]
        );

       Setting "country" element to "US" means that "tv_standard" has a default value set to "NTSC" by the warp
       mechanism.

       Likewise, the warp mechanism enables you to dynamically change the possible values of an enum element:

        state => {
            type => 'leaf',
            value_type => 'enum', # example is admittedly silly
            warp => {
                follow => {
                    c => '- country'
                },
                rules => {
                    '$c eq "US"'        => {
                         choice => ['Kansas', 'Texas' ]
                     },
                    '$c eq "Europe"' => {
                         choice => ['France', 'Spain' ]
                    },
                    '$c eq "Japan"' => {
                         choice => ['Honshu', 'Hokkaido' ]
                    }
                }
            }
        }

   Cascaded warping
       Warping value can be cascaded: "A" can be warped by "B" which can be warped by "C". But this feature
       should be avoided since it can lead to a model very hard to debug. Bear in mind that:

       •   Warp loops are not detected and end up in "deep recursion subroutine" failures.

       •   avoid "diamond" shaped warp dependencies: the results depends on the order of the warp algorithm
           which can be unpredictable in this case

       •   The keys declared in the warp rules ("US", "Europe" and "Japan" in the example above) cannot be
           checked at start time against the warp master "Value". So a wrong warp rule key is silently ignored
           during start up and fails at run time.

Value Reference

       To set up an enumerated value where the possible choice depends on the key of a Config::Model::AnyId
       object, you must:

       •   Set "value_type" to "reference".

       •   Specify the "refer_to" or "computed_refer_to" parameter.  See refer_to parameter.

       In this case, a "IdElementReference" object is created to handle the relation between this value object
       and the referred Id. See Config::Model::IdElementReference for details.

Introspection methods

       The following methods returns the current value of the parameter of the value object (as declared in the
       model unless they were warped):

       min
       max
       mandatory
       choice
       convert
       value_type
       default
       upstream_default
       index_value
       element_name

   name
       Returns the object name.

   get_type
       Returns "leaf".

   can_store
       Returns true if the value object can be assigned to. Return 0 for a read-only value (i.e. a computed
       value with no override allowed).

   get_choice
       Query legal values (only for enum types). Return an array (possibly empty).

   get_help
       With a parameter, returns the help string applicable to the passed value or undef.

       Without parameter returns a hash ref that contains all the help strings.

   get_info
       Returns a list of information related to the value, like value type, default value. This should be used
       to provide some debug information to the user.

       For instance, "$val-"get-info> may return:

        [ 'type: string', 'mandatory: yes' ]

   error_msg
       Returns the error messages of this object (if any)

   warning_msg
       Returns warning concerning this value. Returns a list in list context and a string in scalar context.

   check_value
       Parameters: "( value )"

       Check the consistency of the value.

       "check_value" also accepts named parameters:

       value
       quiet
           When non null, check does not try to get extra information from the tree. This is required in some
           cases to avoid loops in check, get_info, get_warp_info, re-check ...

       In scalar context, return 0 or 1.

       In array context, return an empty array when no error was found. In case of errors, returns an array of
       error strings that should be shown to the user.

   has_fixes
       Returns the number of fixes that can be applied to the current value.

   apply_fixes
       Applies the fixes to suppress the current warnings.

   check
       Parameters: "( [ value => foo ] )"

       Like "check_value".

       Also displays warnings on STDOUT unless "silent" parameter is set to 1.  In this case,user is expected to
       retrieve them with "warning_msg".

       Without "value" argument, this method checks the value currently stored.

   is_bad_mode
       Accept a mode parameter. This function checks if the mode is accepted by "fetch" method. Returns an error
       message if not. For instance:

        if (my $err = $val->is_bad_mode('foo')) {
           croak "my_function: $err";
        }

       This method is intented as a helper to avoid duplicating the list of accepted modes for functions that
       want to wrap fetch methods (like Config::Model::Dumper or Config::Model::DumpAsData)

Information management

   store
       Parameters: "( $value )" or "value => ...,   check => yes|no|skip ), silent => 0|1"

       Store value in leaf element. "check" parameter can be used to skip validation check (default is 'yes').
       "silent" can be used to suppress warnings.

       Optional "callback" is now deprecated.

   clear
       Clear the stored value. Further read returns the default value (or computed or migrated value).

   load_data
       Parameters: "( $value )"

       Called with the same parameters are "store" method.

       Load scalar data. Data is forwarded to "store" after checking that the passed value is not a reference.

   fetch_custom
       Returns the stored value if this value is different from a standard setting or built in setting. In other
       words, returns undef if the stored value is identical to the default value or the computed value or the
       built in value.

   fetch_standard
       Returns the standard value as defined by the configuration model. The standard value can be either a
       preset value, a layered value, a computed value, a default value or a built-in default value.

   has_data
       Return true if the value contains information different from default or upstream default value.

   fetch
       Check and fetch value from leaf element. The method can have one parameter (the fetch mode) or several
       pairs:

       mode
           Whether to fetch default, custom, etc value. See below for details

       check
           Whether to check if the value is valid or not before returning it. Default is 'yes'.  Possible value
           are

           yes Perform check and raise an exception for bad values

           skip
               Perform check and return undef for bad values. A warning is issued when a bad value is skipped.
               Set "check" to "no" to avoid warnings.

           no  Do not check and return values even if bad

       silent
           When set to 1, warning are not displayed on STDOUT. User is expected to read warnings with
           warning_msg method.

       According to the "mode" parameter, this method returns either:

       empty mode parameter (default)
           Value entered by user or default value if the value is different from upstream_default or layered
           value. Typically this value is written in a configuration file.

       backend
           Alias for default mode.

       custom
           The value entered by the user (if different from built in, preset, computed or default value)

       user
           The value most useful to user: the value that is used by the application.

       preset
           The value entered in preset mode

       standard
           The preset or computed or default or built in value.

       default
           The default value (defined by the configuration model)

       layered
           The value found in included files (treated in layered mode: values specified there are handled as
           upstream default values). E.g. like in multistrap config.

       upstream_default
           The upstream_default value. (defined by the configuration model)

       non_upstream_default
           The custom or preset or computed or default value. Returns undef if either of this value is identical
           to the upstream_default value. This feature is useful to reduce data to write in configuration file.

       allow_undef
           With this mode, fetch() behaves like in "user" mode, but returns "undef" for mandatory values.
           Normally, trying to fetch an undefined mandatory value leads to an exception.

   fetch_summary
       Returns a truncated value when the value is a string or uniline that is too long to be displayed.

   user_value
       Returns the value entered by the user. Does not use the default or computed value. Returns undef unless a
       value was actually stored.

   fetch_preset
       Returns the value entered in preset mode. Does not use the default or computed value. Returns undef
       unless a value was actually stored in preset mode.

   clear_preset
       Delete the preset value. (Even out of preset mode). Returns true if other data are still stored in the
       value (layered or user data). Returns false otherwise.

   fetch_layered
       Returns the value entered in layered mode. Does not use the default or computed value. Returns undef
       unless a value was actually stored in layered mode.

   clear_layered
       Delete the layered value. (Even out of layered mode). Returns true if other data are still stored in the
       value (layered or user data). Returns false otherwise.

   get( path => ..., mode => ... ,    check => ... )
       Get a value from a directory like path.

   set( path , value )
       Set a value from a directory like path.

Examples

   Number with min and max values
        bounded_number => {
           type       => 'leaf',
           value_type => 'number',
           min        => 1,
           max        => 4,
        },

   Mandatory value
        mandatory_string => {
           type       => 'leaf',
           value_type => 'string',
           mandatory  => 1,
        },

        mandatory_boolean => {
           type       => 'leaf',
           value_type => 'boolean',
           mandatory  => 1,
        },

   Enum with help associated with each value
       Note that the help specification is optional.

        enum_with_help => {
           type       => 'leaf',
           value_type => 'enum',
           choice     => [qw/a b c/],
           help       => {
               a => 'a help'
           }
        },

   Migrate old obsolete enum value
       Legacy values "a1", "c1" and "foo/.*" are replaced with "a", "c" and "foo/".

        with_replace => {
           type       => 'leaf',
           value_type => 'enum',
           choice     => [qw/a b c/],
           replace    => {
               a1       => 'a',
               c1       => 'c',
               'foo/.*' => 'foo',
           },
        },

   Enforce value to match a regexp
       An exception is triggered when the value does not match the "match" regular expression.

        match => {
           type       => 'leaf',
           value_type => 'string',
           match      => '^foo\d{2}$',
        },

   Enforce value to match a Parse::RecDescent grammar
        match_with_parse_recdescent => {
           type       => 'leaf',
           value_type => 'string',
           grammar    => q{
               token (oper token)(s?)
               oper: 'and' | 'or'
               token: 'Apache' | 'CC-BY' | 'Perl'
           },
        },

   Issue a warning if a value matches a regexp
       Issue a warning if the string contains upper case letters. Propose a fix that translate all capital
       letters to lower case.

        warn_if_capital => {
           type          => 'leaf',
           value_type    => 'string',
           warn_if_match => {
               '/A-Z/' => {
                   fix => '$_ = lc;'
               }
           },
        },

       A specific warning can be specified:

        warn_if_capital => {
           type          => 'leaf',
           value_type    => 'string',
           warn_if_match => {
               '/A-Z/' => {
                   fix  => '$_ = lc;',
                   mesg => 'NO UPPER CASE PLEASE'
               }
           },
        },

   Issue a warning if a value does NOT match a regexp
        warn_unless => {
           type              => 'leaf',
           value_type        => 'string',
           warn_unless_match => {
               foo => {
                   msg => '',
                   fix => '$_ = "foo".$_;'
               }
           },
        },

   Always issue a warning
        always_warn => {
           type       => 'leaf',
           value_type => 'string',
           warn       => 'Always warn whenever used',
        },

   Computed values
       See "Examples" in Config::Model::ValueComputer.

Upgrade

       Upgrade is a special case when the configuration of an application has changed. Some parameters can be
       removed and replaced by another one. To avoid trouble on the application user side, Config::Model offers
       a possibility to handle the migration of configuration data through a special declaration in the
       configuration model.

       This declaration must:

       •   Declare the deprecated parameter with a "status" set to "deprecated"

       •   Declare the new parameter with the instructions to load the semantic content from the deprecated
           parameter. These instructions are declared in the "migrate_from" parameters (which is similar to the
           "compute" parameter)

       Here an example where a URL parameter is changed to a set of 2 parameters (host and path):

        'old_url' => {
           type       => 'leaf',
           value_type => 'uniline',
           status     => 'deprecated',
        },
        'host' => {
           type       => 'leaf',
           value_type => 'uniline',

           # the formula must end with '$1' so the result of the capture is used
           # as the host value
           migrate_from => {
               formula   => '$old =~ m!http://([\w\.]+)!; $1 ;',
               variables => {
                    old => '- old_url'
               },
               use_eval  => 1,
           },
        },
        'path' => {
           type         => 'leaf',
           value_type   => 'uniline',
           migrate_from => {
               formula   => '$old =~ m!http://[\w\.]+(/.*)!; $1 ;',
               variables => {
                    old => '- old_url'
               },
               use_eval  => 1,
           },
        },

EXCEPTION HANDLING

       When an error is encountered, this module may throw the following exceptions:

       Config::Model::Exception::Model Config::Model::Exception::Formula Config::Model::Exception::WrongValue
       Config::Model::Exception::WarpError

       See Config::Model::Exception for more details.

AUTHOR

       Dominique Dumont, (ddumont at cpan dot org)

SEE ALSO

       Config::Model, Config::Model::Node, Config::Model::AnyId, Config::Model::Warper, Config::Model::Exception
       Config::Model::ValueComputer,

AUTHOR

       Dominique Dumont

       This software is Copyright (c) 2005-2022 by Dominique Dumont.

       This is free software, licensed under:

         The GNU Lesser General Public License, Version 2.1, February 1999