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Object::Pad::FieldAttr::Final(3pm) | User Contributed Perl Documentation | Object::Pad::FieldAttr::Final(3pm) |
NAME¶
"Object::Pad::FieldAttr::Final" - declare "Object::Pad" fields readonly after construction
SYNOPSIS¶
use Object::Pad; use Object::Pad::FieldAttr::Final; class Rectangle { has $width :param :reader :Final; has $height :param :reader :Final; has $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¶
has $field :Final ...; has $field :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.
has $field :Final; ADJUST { $field = 123; } # this is permitted method m { $field = 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.
has $aref :Final; ADJUST { $aref = []; } method more { push @$aref, "another"; } # this is permitted
AUTHOR¶
Paul Evans <leonerd@leonerd.org.uk>
2022-10-20 | perl v5.36.0 |