NAME

       UR::Role::Param - Role parameters as package variables

SYNOPSIS

         package ProjectNamespace::LoggingRole;
         use ProjectNamespace;

         our $logging_object : RoleParam(logging_obejct);
         role ProjectNamespace::SomeParameterizedRole { };

         sub log {
             my($self, $message) = @_;
             $logging_object->log($message);
         }

         package ThingThatLogs;
         my $logger = create_a_logging_object();
         class ThingThatLogs {
             roles => [ ProjectNamespace::SomeParameterizedRole->create(logging_object => $logger) ],
         };

DESCRIPTION

       Roles can be configured by declaring variabls with the "RoleParam" attribute.  These
       variables acquire values by calling "create()" on the role's name and giving values for
       all the role's parameters.  More information about declaring and using these parameters is
       described in the "Parameterized Roles" section of UR::Role.

       When the variables are initially declared, their value is initialized to a reference to a
       UR::Role::Param.  This represents a placeholder value to be filled in later.  The value
       may be used in a role definition or in any subroutine.

       When the role is composed into a class, the placeholder values are replaced with the
       actual values given in the "create()" call on the role's name.  The original RoleParam
       variable is then tied to the UR::Role::Param class; it's "FETCH" method returns the proper
       value by searching the call stack for the first method whose invocant class has composed
       the role where the FETCH originated from.  It returns the value given when the role was
       composed into the class.

       These role param variables are read-only.

       Each variable with the RoleParam attribute becomes a required argument when the role is
       instantiated .

SEE ALSO

       UR::Role, UR::Role::Prototype, UR::Role::Instance