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NAME
Object::Pad::FieldAttr::LazyInit - lazily initialise Object::Pad fields
at first read
SYNOPSIS
use Object::Pad;
use Object::Pad::FieldAttr::LazyInit;
class Item {
field $uuid :reader :param :LazyInit(_make_uuid);
method _make_uuid {
require Data::GUID;
return Data::GUID->new->as_string;
}
}
DESCRIPTION
This module provides a third-party field attribute for
Object::Pad-based classes, which declares that the field it is attached
to has a lazy initialisation method, which will be called the first
time the field's value is read from.
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
:LazyInit
field $name :LazyInit(NAME) ...;
Declares that if the field variable is read from before it has been
otherwise initialised, then the named method will be called first to
create an initial value for it. Initialisation by either by a :param
declaration, explicit assignment into it, or the use of a :writer
accessor will set the value for the field and mean the lazy initialiser
will not be invoked.
After it has been invoked, the value is stored by the field and
thereafter it will behave as normal; subsequent reads will return the
current value, and the initialiser method will not be invoked again.
In order to avoid the possibility of accidental recursion when
generating the value, it is recommended that the logic in the lazy
initialisation method be as self-contained as possible; ideally not
invoking any methods on $self, and only making use of other fields
already declared before the field being initialised. By placing the
initialiser method immediately after the field declaration, before any
other fields, you can reduce the possibility of getting stuck in such a
manner.
field $field_zero :param;
field $field_one :LazyInit(_make_one);
method _make_one {
# we can safely use $field_zero in here
}
field $field_two :LazyInit(_make_two);
method _make_two {
# we can safely use $field_zero and $field_one
}
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>
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