NAME

"Object::Pad::FieldAttr::Final" - declare "Object::Pad" fields readonly after construction

SYNOPSIS

   use Object::Pad;
   use Object::Pad::FieldAttr::Final;
   class Rectangle {
      field $width  :param :reader :Final;
      field $height :param :reader :Final;
      field $area :reader :Final;
      ADJUST {
         $area = $width * $height;
      }
   }

DESCRIPTION

This module provides a third-party field attribute for Object::Pad-based classes, which declares that the field it is attached to shall be set as readonly when the constructor returns, disallowing further modification to it.

WARNING The ability for Object::Pad to take third-party field attributes is still new and highly experimental, and subject to much API change in future. As a result, this module should be considered equally experimental.

FIELD ATTRIBUTES

:Final

   field $name :Final ...;
   field $name :Final ... = DEFAULT;

Declares that the field variable will be set readonly at the end of the constructor, after any assignments from ":param" declarations or "ADJUST" blocks. At this point, the value cannot otherwise be modified by directly writing into the field variable.

   field $x :Final;
   ADJUST { $x = 123; }    # this is permitted
   method m { $x = 456; }  # this will fail

Note that this is only a shallow readonly setting; if the field variable contains a reference to a data structure, that structure itself remains mutable.

   field $aref :Final;
   ADJUST { $aref = []; }
   method more { push @$aref, "another"; }   # this is permitted

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>