Moose: Expiring cached results of calculations when attribute values change? - perl

In our classes we have a pattern where we create an attribute to represent a
calculated value. For obvious reasons we want to cache the calculated value
and then invalidate the cache when one of the underlying values change.
So we currently have this:
package FooBar;
use Moose;
has 'foo' => (
accessor => {
'foo' => sub {
my $self = shift;
if (#_ > 0) {
# writer
$self->{foo} = $_[0];
# reset fields that are dependant on me
$self->{bar} = undef;
}
# reader part;
return $self->{foo};
}
}
);
has 'bar' => (
accessor => {
'bar' => sub {
my $self = shift;
if (#_ > 0) {
# writer
$self->{bar} = $_[0];
}
# reader part;
$self->{bar} = calculate_bar($self->foo, $self->baz)
if (not defined($self->{bar}));
return $self->{bar};
}
}
);
sub calculate_bar { ... }
This long hand method is getting very tedious and error prone when calculated values
depend on other calculated values.
Is there a smarter/simpler way for 'bar' to monitor the attributes it depends on
vs having 'foo' know who is dependent on it? Also how can I avoid setting bar via hash
member access?

If I understand you correctly, you can use triggers to clear attributes when one is set. Here's an example:
has 'foo' => (
is => 'rw',
trigger => sub{
my ($self) = #_;
$self->clear_bar;
}
);
has 'bar' => (
is => 'rw',
clearer => 'clear_bar',
lazy => 1,
default => sub{
my ($self) = #_;
return calculate_bar( ... );
}
);
So, any writes to foo via $obj->foo($newvalue) will cause bar to be cleared, and recreated on next access.

I think it is quite possible that you're making this harder on yourself by using an Attributes implicit memoization with lazy, when you could just make the memoization explicit making your whole program more transparent
has [qw/foo bar baz/] => ( isa => 'Value', is => 'rw' );
use Memoize;
memoize('_memoize_this');
sub old_lazy_attr {
my $self = shift;
_memoize_this( $self->attr1, $self->attr2, $self->attr3 );
}
sub _memoize_this {
my #args = #_;
# complex stuff
return $result
}
See cpan's Memoize for information and control of the internal cache, also remember that a Memoized function can not be dependent on the state of the object. So the arguments must be passed in explicitly.

Would this work?
#!/usr/bin/perl
package Test;
use Modern::Perl;
use Moose;
has a => (is => 'rw', isa => 'Str', trigger => \&change_a);
has b => (is => 'rw', isa => 'Str', trigger => \&change_b);
has c => (is => 'rw', isa => 'Str');
sub change_a
{
my $self = shift;
say 'update b';
$self->b($self->a . ', bar');
}
sub change_b
{
my $self = shift;
say 'update c';
}
package main;
my $test = Test->new->a('Foo');
Output:
$ perl test.pl
update b
update c

I haven't done any poking around in Moose internals and the meta object protocol, but I think this is a good time to do it.
You want to patch the code generation so that when you specify an attribute as
has 'foo' => ();
has 'bar' => (
depends_on => [qw( foo )],
lazy => \&calculate_bar,
);
the code generation phase creates code for the foo and bar attributes as you specified above.
How to do this is an exercise left to the reader. If I had a clue, I'd try to give you a start. Unfortunately, all I can advise you with is "This is a job for the MOP".

Related

Better way to get all attributes from a Moose class as a hash

I want to get all attributes back from a class as a hash.
Is there any better way to do it than this ?
Ideally(?) I would like to be able to say something like:
my $hash = \%{ Diag->new( {range =>1, code => 'AB'} ) };
But will settle for:
my $d = Diag->new( {range =>1, code => 'AB'} );
my $hash = $d->hash;
package Diag;
use Moose;
my #attrs = qw/range code severity source message/;
has 'range' => ( is => 'rw', isa => 'Int' );
has 'code' => ( is => 'rw', isa => 'String' );
has 'severity' => ( is => 'rw', isa => 'Int' );
has 'source' => ( is => 'rw', isa => 'String' );
has 'message' => ( is => 'rw', isa => 'String' );
sub hash {
my $self = shift;
my $hash = {};
for (#attrs) {
$hash->{$_} = $self->$_;
}
return $hash;
}
no Moose;
1;
EDIT Hash with string output for pack/unpack:
# Combining this attribute and the record_format would be great.
# if $self->record->format worked that would be cool.
has 'record' => (
is => 'ro',
isa => 'HashRef',
default => sub {
{
foo => 'A5',
foo2 => 'A16',
}
);
sub record_format
{
my $self = shift;
my #fields = qw( foo foo2 );
return _build_format_string($self->record, \#fields);
}
sub _build_format_string {
return join '', map { $_[1]->{$_} } #{ $_[2] };
}
EDIT2
I found that if I created an Attribute Trait I could make this a little nicer. This way the hash order is with the attribute and only one format method is needed.
package Order;
use Moose::Role;
has order => (
is => 'ro',
isa => 'ArrayRef',
predicate => 'has_order',
);
Moose::Util::meta_attribute_alias('Order');
1;
package Record;
use Moose;
has 'record' => (
traits => [qw/Order/],
is => 'ro',
isa => 'HashRef',
default => sub {
{
foo => 'A5',
foo2 => 'A16',
},
;
},
order => [qw(foo foo2)]
);
sub format {
my ( $self, $attr ) = #_;
my $fields = $self->meta->get_attribute($attr)->order();
return join '', map { $self->{$attr}{$_} } #$fields;
}
1;
my $r = Record->new();
print $r->format("record");
Outputs: A5A16
I would much rather pack that into a method, but your "ideal" case is almost there
my $data = { %{ Diag->new( {range =>1, code => 'AB'} ) } };
The %{...} returns a (key,value,...) list so you want {} to make a hashref out of it, not \ (which curiously turns it back into an object).
But really, that should be tucked away in a method
my $data = Diag->new(...)->get_data;
package Diag;
...
sub get_data { return { %{$_[0]} } };
...
1;
For purely presentational purposes – to print them out – consider using a module, so you don't have to worry about (or know) which attributes have what reference as a value. I use Data::Dump for conciseness of its output
my $obj = Diag->new(...);
say $obj->stringify(); # whole object serialized
say for $obj->stringify('attr1', 'attr1', ...); # serialized values for each
package Diag;
...
use Data::Dump qw(pp);
...
sub stringify {
my $self = shift;
return map { pp $self->{$_} } #_ if #_;
return { pp %$self } }
}
If native OO is used and not Moo/Moose also overload "" for say $obj; use
use overload q("") => sub { return shift->stringify() }
In Moo and Moose the stringification of object under "" (implied in prints as well) is provided.
By further clarifications the code below doesn't address the actual problem. I'll edit but I am leaving this for now as it was deemed generally useful.
It has come up in comments and question edit that a part of the intent is to be able to retrieve values for attribute(s) as well, and packed. The added code does that, but as there is explicit dereferencing a check with ref should be added so to correctly retrieve all values, from either of arrayref, hashref, or string/number. For example
sub record_format {
my ($self, #attrs) = #_;
#attrs = qw(attr1 attr2 ...) if not #attrs; # default list
my $packed;
foreach my $attr (#attrs) {
my $val = $self->{$attr};
my $rv = ref $val;
if (not $rv) { $packed .= $val }
elsif ($rv eq 'HASH') { $packed .= join '', values %$val }
elsif ($rv eq 'ARRAY') { $packed .= join '', #$val }
}
return $packed;
}
This packs values of the passed attributes or of the listed defaults.
The desired $self->record->format can't work nicely since $self->record doesn't return an object so you can't string another method call. You can write an accessor but if you made it return an object under any circumstances that would likely be a surprising behavior, thus not good design.

How can I provide an alternate init arg for an attribute in Moose?

I of course know that I can rename the init arg for an attribute by setting init_arg (e.g)
package Test {
use Moose;
has attr => (
is => 'ro',
isa => 'Str',
init_arg => 'attribute'
);
}
which would allow me to
Test->new({ attribute => 'foo' });
but not
Test->new({ attr => 'foo' });
at the same time
MooseX::Aliases actually has this behavior, but creating an alias also creates accessors. I'm currently trying to understand the code in that module to see if I can't determine how it does it, so that I can replicate said functionality (in a way I understand). If someone could explain how to do it here with an example that'd be great.
update it appears that MX::Aliases is doing this by way of replacing what's actually passed to the constructor in an around initialize_instance_slot but I'm still not sure how that's actually getting called, because in my test code my around isn't actually getting executed.
update munging in BUILDARGS isn't really an option because what I'm trying to do allow setting of the accessor via the name of the label I'm adding to the attribute via Meta Recipe3. You might say I'm doing
has attr => (
is => 'ro',
isa => 'Str',
alt_init_arg => 'attribute'
);
update
here's what I've managed to work out with what I'm trying to do so far.
use 5.014;
use warnings;
package MooseX::Meta::Attribute::Trait::OtherName {
use Moose::Role;
use Carp;
has other_name => (
isa => 'Str',
predicate => 'has_other_name',
required => 1,
is => 'ro',
);
around initialize_instance_slot => sub {
my $orig = shift;
my $self = shift;
my ( $meta_instance, $instance, $params ) = #_;
confess 'actually calling this code';
return $self->$orig(#_)
unless $self->has_other_name && $self->has_init_arg;
if ( $self->has_other_name ) {
$params->{ $self->init_arg }
= delete $params->{ $self->other_name };
}
};
}
package Moose::Meta::Attribute::Custom::Trait::OtherName {
sub register_implementation { 'MooseX::Meta::Attribute::Trait::OtherName' }
}
package Message {
use Moose;
# use MooseX::StrictConstructor;
has attr => (
traits => [ 'OtherName' ],
is => 'ro',
isa => 'Str',
other_name => 'Attr',
);
__PACKAGE__->meta->make_immutable;
}
package Client {
use Moose;
sub serialize {
my ( $self, $message ) = #_;
confess 'no message' unless defined $message;
my %h;
foreach my $attr ( $message->meta->get_all_attributes ) {
if (
$attr->does('MooseX::Meta::Attribute::Trait::OtherName')
&& $attr->has_other_name
) {
$h{$attr->other_name} = $attr->get_value( $message );
}
}
return \%h;
}
__PACKAGE__->meta->make_immutable;
}
my $message = Message->new( Attr => 'foo' );
my $ua = Client->new;
my %h = %{ $ua->serialize( $message )};
use Data::Dumper::Concise;
say Dumper \%h
problem is that my around block is never being run and I'm not sure why, maybe I'm wrapping it in the wrong place or something.
MooseX::Aliases has several moving parts to make this functionality happen, that's because the behavior needs to be applied to several different places in the MOP. Your code here looks very close to the code in MooseX::Aliases's Trait attribute.
I suspect the reason your code isn't being called is due to something going wrong when you try to register your trait. MooseX::Aliases uses Moose::Util::meta_attribute_alias rather than the old fashioned way you're using here. Try replacing your Moose::Meta::Attribute::Custom::Trait::OtherName section with a call to Moose::Util::meta_attribute_alias 'OtherName'; inside your Role.
Second the code you have here won't work for immutable classes. You'll need to add a second trait to handle those because the immutability code is handled by the class's metaclass and not the attribute's metaclass. You'll need to add some more traits to handle attributes in Roles as well I think. Then you'll need to wire up an Moose::Exporter to make sure that all the traits are applied properly when everything is compiled.
I've gotten a simple version of this working up through immutable. This code is also on github.
First the Attribute trait:
package MooseX::AltInitArg::Meta::Trait::Attribute;
use Moose::Role;
use namespace::autoclean;
Moose::Util::meta_attribute_alias 'AltInitArg';
has alt_init_arg => (
is => 'ro',
isa => 'Str',
predicate => 'has_alt_init_arg',
);
around initialize_instance_slot => sub {
my $orig = shift;
my $self = shift;
my ($meta_instance, $instance, $params) = #_;
return $self->$orig(#_)
# don't run if we haven't set any alt_init_args
# don't run if init_arg is explicitly undef
unless $self->has_alt_init_arg && $self->has_init_arg;
if (my #alternates = grep { exists $params->{$_} } ($self->alt_init_arg)) {
if (exists $params->{ $self->init_arg }) {
push #alternates, $self->init_arg;
}
$self->associated_class->throw_error(
'Conflicting init_args: (' . join(', ', #alternates) . ')'
) if #alternates > 1;
$params->{ $self->init_arg } = delete $params->{ $alternates[0] };
}
$self->$orig(#_);
};
1;
__END__
Next the Class trait.
package MooseX::AltInitArg::Meta::Trait::Class;
use Moose::Role;
use namespace::autoclean;
around _inline_slot_initializer => sub {
my $orig = shift;
my $self = shift;
my ($attr, $index) = #_;
my #orig_source = $self->$orig(#_);
return #orig_source
# only run on aliased attributes
unless $attr->meta->can('does_role')
&& $attr->meta->does_role('MooseX::AltInitArg::Meta::Trait::Attribute');
return #orig_source
# don't run if we haven't set any aliases
# don't run if init_arg is explicitly undef
unless $attr->has_alt_init_arg && $attr->has_init_arg;
my $init_arg = $attr->init_arg;
return (
'if (my #aliases = grep { exists $params->{$_} } (qw('
. $attr->alt_init_arg . '))) {',
'if (exists $params->{' . $init_arg . '}) {',
'push #aliases, \'' . $init_arg . '\';',
'}',
'if (#aliases > 1) {',
$self->_inline_throw_error(
'"Conflicting init_args: (" . join(", ", #aliases) . ")"',
) . ';',
'}',
'$params->{' . $init_arg . '} = delete $params->{$aliases[0]};',
'}',
#orig_source,
);
};
1;
__END__
Finally the Moose::Exporter glue.
package MooseX::AltInitArg;
use Moose();
use Moose::Exporter;
use MooseX::AltInitArg::Meta::Trait::Attribute;
Moose::Exporter->setup_import_methods(
class_metaroles => { class => ['MooseX::AltInitArg::Meta::Trait::Class'] }
);
1;
__END__
An example of how this is used then:
package MyApp;
use 5.10.1;
use Moose;
use MooseX::AltInitArg;
has foo => (
is => 'ro',
traits => ['AltInitArg'],
alt_init_arg => 'bar',
);
my $obj = MyApp->new( bar => 'bar' );
say $obj->foo; # prints bar
Meta-Programming in Moose is incredibly powerful, but because there are a lot of moving parts (many of which have solely to do with maximizing performance) you bite off a lot of work when you dive in.
Good luck.
I could be wrong but I think you might be able to accomplish what I think you are trying to do using the BUILDARGS method. This lets you munge the contructor arguments before they are used to create the object.
#!/usr/bin/env perl
use strict;
use warnings;
{
package MyClass;
use Moose;
has attr => (
is => 'ro',
isa => 'Str',
required => 1,
);
around BUILDARGS => sub {
my $orig = shift;
my $self = shift;
my %args = ref $_[0] ? %{shift()} : #_;
if (exists $args{attribute}) {
$args{attr} = delete $args{attribute};
}
$self->$orig(%args);
};
}
my $one = MyClass->new(attribute => "Hi");
my $two = MyClass->new(attr => "Bye");
print $one->attr, "\n";
print $two->attr, "\n";
So what I'm hearing is that:
At construction time, an attribute should be able to be set by its init_arg and any alternate init_args defined on the attribute.
An attribute should not be able to be manipulated by its alternate init_args except at instance construction; that is, aside from the above, the attribute should behave "normally".
Based on that, this seems like a good match for the MooseX::MultiInitArg attribute trait. Yes? :)

Moose around method modifier, setter and constructor (new): intercept all updates to an attribute

Update
The code I posted in my original question was illustrative of the way method modifier do or don't work.
It was not necessarily illustrative of the problem description I gave.
This code should be. It works, but contains a hack in the trigger I used to code the requirement of tracking all updates and acting upon them based on the value supplied to the setter.
package Article;
use Moose;
use Moose::Util::TypeConstraints;
has 'name', is => 'rw', isa => 'Str', required => 1;
has 'price', is => 'rw', isa => 'Num', required => 1;
has 'quantity', is => 'rw', isa => 'Num', required => 1,
trigger => \&update_quantity;
has 'quantity_original', is => 'rw', isa => 'Num',
predicate => 'quantity_fix',
clearer => 'quantity_back_to_normal';
# https://metacpan.org/module/Moose::Cookbook::Basics::Recipe3
# A trigger accepts a subroutine reference, which will be called as a method
# whenever the attribute is set. This can happen both during object
# construction or later by passing a new object to the attribute's accessor
# method. However, it is not called when a value is provided by a default or
# builder.
sub update_quantity {
my( $self, $val ) = #_;
# print STDERR $val, "\n";
if ( $val == int $val ) {
$self->quantity_back_to_normal;
} else {
$self->quantity_original( $val );
# Updating quantity via setter would retrigger this code.
# Which would defeat its purpose. The following won't:
$self->{quantity} = 1; # hack, yes; but it does work
}
}
around name => sub {
my $orig = shift;
my $self = shift;
return $self->$orig( #_ ) if #_; # setter
return $self->$orig unless $self->quantity_fix;
return sprintf '%s (%s)', $self->$orig, $self->quantity_original;
};
around price => sub {
my $orig = shift;
my $self = shift;
return $self->$orig( #_ ) if #_; # setter
return $self->$orig unless $self->quantity_fix;
return int( 100 * $self->$orig * $self->quantity_original + 0.5 ) / 100;
};
__PACKAGE__->meta->make_immutable; no Moose;
package main;
use Test::More;
{ my $art = Article->new( name => 'Apfel', price => 33, quantity => 4 );
is $art->price, 33, 'supplied price';
is $art->quantity, 4, 'supplied quantity';
is $art->name, 'Apfel', 'supplied name';
}
{ my $art = Article->new( name => 'Mehl', price => 33, quantity => 4.44 );
# diag explain $art;
is $art->quantity, 1, 'has quantity fixed';
is $art->price, 33 * 4.44, 'has price fixed';
is $art->name, 'Mehl (4.44)', 'has name fixed';
# tougher testing ...
$art->quantity(3);
is $art->quantity, 3, 'supplied quantity again';
is $art->price, 33, 'supplied price again';
is $art->name, 'Mehl', 'supplied name again';
}
done_testing;
Still not sure what Moose facility to employ to do the job.
An abundance of features and facilities does not always make things easier.
At least not when you try not to reinvent any wheels and reuse what can be reused.
Original question
It appears the around method modifier isn't called as part of building the object (when calling new). Test case here:
package Bla;
use Moose;
has 'eins', is => 'rw', isa => 'Int';
has 'zwei', is => 'rw', isa => 'Num';
around [qw/ eins zwei /] => sub {
my $orig = shift;
my $self = shift;
return $self->$orig unless #_;
my $val = shift;
if ( $val == int $val ) {
return $self->$orig( $val );
}
else {
return $self->$orig( 1 );
warn "replaced $val by 1";
}
};
package main;
use Test::More;
use Test::Exception;
dies_ok { Bla->new( eins => 33.33 ) } 'dies because of Int type constraint';
my $bla = Bla->new( zwei => 22.22 );
is $bla->zwei, 22.22, 'around has not been called';
done_testing;
Let me explain what I want to achieve. There's a class that has quantity and price (and some more state). When quantity comes in (via new or the setter, I don't care), I want to make sure it ends up as an integer (hence the constraint). If it's not an integer, I want to replace it by just 1 and make some other updates to the object, like saving the original quantity and multiplying the price by the original quantity. Both for the constructor and the setter.
What should I do? Provide a subroutine that does the job and call it from both around BUILDARGS and around quantity?
How about this?
package Bla;
use Moose;
use Moose::Util::TypeConstraints;
subtype 'MyInt',
as 'Int';
coerce 'MyInt',
from 'Num',
via { 1 };
has 'eins', is => 'rw', isa => 'Int';
has 'zwei', is => 'rw', isa => 'MyInt', coerce => 1;
package main;
use Test::More;
use Test::Exception;
dies_ok { Bla->new( eins => 33.33 ) } 'dies because of Int type constraint';
my $bla = Bla->new( zwei => 22.22 );
is $bla->zwei, 1, '22.22 -> 1';
my $bla2 = Bla->new( zwei => 41 );
is $bla2->zwei, 41, '41 -> 41';
done_testing;
When I keep running against walls, I know I did something wrong, and I'm running against walls. The design sucks. I think the key problem is that you have one field serving two purposes.
If the only purpose of orig_quantity is to normalize the price, I suggested that you normalize quantity and price after they are set. This could be done explicitly, or it could be done implicitly when you try to fetch them as shown below.
has price => (
accessor => '_price',
isa => 'Num',
handles => {
price => sub {
my $self = shift;
return $self->_price(#_) if #_;
$self->normalize();
return $self->_price();
},
},
);
has quantity => (
accessor => '_quantity',
isa => 'Num',
handles => {
quantity => sub {
my $self = shift;
return $self->_quantity(#_) if #_;
$self->normalize();
return $self->_quantity();
},
},
);
sub normalize {
my ($self) = #_;
my $quantity = $self->_quantity();
return if is_an_int($quantity);
$self->_quantity(1);
$self->_price($self->_price() / $quantity);
}
If you actually do need orig_quantity, then you probably want the constructor to set this directly and make quantity a derived value.

Perl, #array in perl constructor

I write perl classes, but I don't know how to have a array or a hash in my $this variable ?
I have a pack.pm :
#!/usr/bin/perl -w
use strict;
use Parallel::ForkManager;
package Pack;
our $cgi = new CGI;
sub new {
my ($classe, $nom, $nbports, $gio) = #_;
my $this = {
"nom" => $nom,
"nbports" => $nbports,
"gio" => $gio
};
bless($this, $classe);
return $this;
}
...
1;
I would like to have a #tab, I can access via $this->tab, but I don't want to give it in arg to the instance.
How does it work in Perl ?
Thanks.
Given your answer to my comments, I think you want
my($this) = {
"nom" => $nom,
"nbports" => $nbports,
"gio" => $gio,
"tab" => []
};
i.e. set $this->{tab} to be a reference to a new anonymous array.
Now you can reference it as you wish, e.g.
$this->{"tab"}[0] = "new value";
print "Table contains ", scalar(#{$this->{"tab"}}), "entries\n";
Consider using Moose for your OO Perl needs.
I've created a Moose version of your object that includes an attribute with an attribute featuring Array trait delegation, inlcuding currying of delegated methods. Moose offers easy ways to generate powerful, encapsulated classes without writing reams of boilerplate.
I created a class Pack with attributes: nom, nbports, gio, and tab.
nom is a read-only string and is required when the object is created.
nbports is a read-only integer value and defaults to 32 when not provided.
gio is an optional, read-write boolean value.
tab is an array of strings. All sorts of behavior has been defined for tab:
all_tabs returns a list of the contents of tabs
add_tab pushes values onto the end of tabs
tab_count returns a count of the elements in tabs
alpha_tabs returns a list of the members of tabs alphabetical order
turn_tabs returns a list of the strings in tabs, but with the letters in reverse
Any attempts to set an attribute with be checked for type correctness.
Moose creates all the required methods to support these complex behaviors with the following code:
package Pack;
use Moose;
has 'nom' => (
is => 'ro',
isa => 'Str',
required => 1,
);
has 'nbports' => (
is => 'ro',
isa => 'Int',
default => 32,
);
has 'gio' => (
is => 'rw',
isa => 'Bool',
predicate => 'has_gio',
);
has 'tab' => (
traits => ['Array'],
is => 'ro',
isa => 'ArrayRef[Str]',
default => sub {[]},
handles => {
all_tabs => 'elements',
add_tab => 'push',
turn_tabs => [ 'map', sub { reverse } ],
tab_count => 'count',
alpha_tabs => [ 'sort', sub { lc($a) cmp lc($b) } ],
},
);
__PACKAGE__->meta->make_immutable;
no Moose;
1;
Usable like so:
my $p = Pack->new( nom => 'Roger', tab => [qw( fee fie foe fum )] );
my $gio_state = 'UNSET';
if( $p->has_gio ) {
$gio_state = $p->gio ? 'TRUE' : 'FALSE';
}
print "GIO is $gio_state\n";
my #turned = $p->turn_tabs; # eef eif eof muf
$p->add_tabs( 'faa', 'fim' );
my #sorted = $p->alpha_tabls; # faa fee fie fim foe fum
my $count = $p->tab_count; # 6
my $ports = $p->nbports; # 32
try with:
sub set_tab {
my ($self, #tab) = #_;
$self->{ tab } = \#tab;
}

Moose: Loading object from file in the BUILD method

I have to read a file in the BUILD method and I want to use the load method of the MooseX::Storage package.
But this load method create a new object and so when I instatiate the object this isn’t the object read from file. In the code below I create an object $m1 with state 2 to write the file, I create $m2 with no parameter to read the file but $m2 doesn’t contain the right value.
The package:
package mia;
use Moose;
use MooseX::Storage;
with Storage(format => 'JSON', io => 'File');
has 'nome' => ( is => 'rw', isa => 'Str', default =>'',);
has 'stato' => ( is => 'rw', isa => 'Int', default =>1,);
sub BUILD {
my $self=shift;
if ($self->stato==1){
$self=mia->load("mia.dat");
}
if ($self->stato==2){
$self->stato(0);
$self->nome("prova");
$self->store("mia.dat");
}
}
sub stampa(){
my $self=shift;
print $self->nome." ".$self->stato;
}
the main program
use mia;
my $m;
$m1=mia->new(stato=>2);
$m2=mia->new();
print "\nm1 \n";
$m1->stampa();
print "\nm2 \n";
$m2->stampa();
Your code seems to be acting as if BUILD is a constructor, which it isn't -- it's more like a post-construction hook where you can perform other things like read values from a DB. You should instead either:
store the result of mia->load in an attribute, and optionally use delegated methods to access it, or
use the result of mia->load as the object, rather than constructing a separate one.
Here is an example of the first case, separating the MooseX::Storage object from the object that controls it:
package miaController;
use Moose;
use mia;
has 'nome' => ( is => 'rw', isa => 'Str', default =>'',);
has 'stato' => ( is => 'rw', isa => 'Int', default =>1,);
has 'mia' => ( is => 'rw', isa => 'mia', lazy => 1);
sub BUILD
{
my $self = shift;
if ($self->stato == 1)
{
$self->mia(mia->load("mia.dat"));
}
elsif ($self->stato == 2)
{
$self->stato(0);
$self->nome("prova");
$self->mia->store("mia.dat");
}
}
sub stampa
{
my $self = shift;
print $self->nome." ".$self->stato;
}
package mia;
use Moose;
use MooseX::Storage;
with Storage(format => 'JSON', io => 'File');
package main:
use miaController;
my $m1=miaController->new(stato=>2);
my $m2=miaController->new();
print "\nm1 \n";
$m1->stampa();
print "\nm2 \n";
$m2->stampa();