Config::Model::ValueComputer - Provides configuration value computation
version 1.225
my $model = Config::Model->new() ; $model ->create_config_class ( name => "Master", element => [ [qw/av bv/] => {type => 'leaf', value_type => 'integer', }, compute_int => { type => 'leaf', value_type => 'integer', compute => { formula => '$a + $b', variables => { a => '- av', b => '- bv'} }, min => -4, max => 4, }, [qw/sav sbv/] => {type => 'leaf', value_type => 'string', }, compute_string => { type => 'leaf', value_type => 'string', compute => { formula => 'meet $a and $b', variables => { '- sav', b => '- sbv' } }, }, compute_with_replace => { type => 'leaf', value_type => 'string', compute => { formula => '$replace{$who} is the $replace{$what} of $replace{$country}', variables => { who => '! who' , what => '! what' , country => '- country', }, replace => { chief => 'president', America => 'USA' }, }, }, url => { type => 'leaf', value_type => 'uniline'}, extract_host_from_url => { type => 'leaf', value_type => 'uniline', compute => { formula => '$old =~ m!http://([\w\.]+)!; $1 ;' , variables => { old => '- url' } , use_eval => 1 , }, }, ] ) ;
This class provides a way to compute a configuration value. This computation uses a formula and some other configuration values from the configuration tree.
The computed value can be overridden, in other words, the computed value can be used as a defult value.
A computed value must be declared in a 'leaf' element. The leaf element must have a compute argument pointing to a hash ref.
compute
This array ref contains:
A string formula that use variables and replace function.
A set of variable and their relative location in the tree (using the notation explained in grab() method
An optional set of replace rules.
An optional parameter to force a Perl eval of a string.
The first element of the compute array ref must be a string that contains the computation algorithm (i.e. a formula for arithmetic computation for integer values or a string template for string values).
This string or formula should contain variables (like $foo or $bar). Note that these variables are not interpolated by perl.
$foo
$bar
For instance:
'My cat has $nb legs' '$m * $c**2'
This string or formula may also contain:
The index value of the current object : &index or &index().
&index
&index()
The index value of another object: &index($other)
&index($other)
The element name of the current object: &element or &element().
&element
&element()
The element name of another object: &element($other)
&element($other)
For instance, you could have this template string:
'my element is &element, my index is &index' . 'upper element is &element($up), upper index is &index($up)',
If you need to perform more complex operations than substition, like extraction with regular expressions, you can force an eval done by Perl with use_eval => 1. In this case, the result of the eval will be used as the computed value.
use_eval => 1
# extract host from url compute => { formula => '$old =~ m!http://[\w\.]+(?::\d+)?(/.*)!; $1 ;', variables => { old => '- url' } , use_eval => 1 , }, # capitalize compute => { formula => 'uc($old)', variables => { old => '- small_caps' } , use_eval => 1 }
The following arguments will be a set of key => value to define the variables used in the formula. The key is a variable name used in the computation string. The value is a string that will be used to get the correct Value object.
key => value
In this numeric example, result default value is av + bv:
result
av + bv
element => [ av => { type => 'leaf', value_type => 'integer' }, bv => { type => 'leaf', value_type => 'integer' }, result => { type => 'leaf', value_type => 'integer', compute => { formula => '$a + $b' , variables => { a => '- av', b => '- bv' }, } }
In this string example, the default value of the Comp element is actually a string made of "macro is " and the value of the "macro" element of the object located 2 nodes above:
Comp
macro is
macro
comp => { type => 'leaf', value_type => 'string', compute => { formula => '"macro is $m"' , variables => { m => '- - macro' } } }
Sometime, using the value of a tree leaf is not enough and you need to substitute a replacement for any value you can get. This replacement can be done using a hash like notation within the formula using the %replace hash.
%replace
For instance, if you want to display a summary of a config, you can do :
compute_with_replace => { formula => '$replace{$who} is the $replace{$what} of $replace{$country}', variables => { who => '! who' , what => '! what' , country => '- country', }, replace => { chief => 'president', America => 'USA' },
&index, &element, and replace can be combined. But the argument of &element or &index can only be a value object specification (I.e. something like '- - foo'), it cannot be a value replacement of another &element or &index.
- - foo
I.e. &element($foo) is ok, but &element(&index($foo)) is not allowed.
&element($foo)
&element(&index($foo))
Compute variables can themselves be computed :
compute => { formula => 'get_element is $replace{$s}, indirect value is \'$v\'', variables => { 's' => '! $where', where => '! where_is_element', v => '! $replace{$s}', } replace => { m_value_element => 'm_value', compute_element => 'compute' } }
Be sure not to specify a loop when doing recursive computation.
In some case, a computed value must be interpreted as a default value and the user must be able to override this computed default value. In this case, you must use allow_override => 1 with the compute parameter:
allow_override => 1
computed_value_with_override => { type => 'leaf', value_type => 'string', compute => { formula => '"macro is $m"' , variables => { m => '- - macro' } , allow_override => 1, } }
Dominique Dumont, (ddumont at cpan dot org)
Config::Model, Config::Model::Instance, Config::Model::Value
To install Config::Model, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Config::Model
CPAN shell
perl -MCPAN -e shell install Config::Model
For more information on module installation, please visit the detailed CPAN module installation guide.