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Id: 27060
Status: resolved
Priority: 0/
Queue: Object-InsideOut

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Owner: Nobody in particular
Requestors: polettix [...] cpan.org
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Bug Information
Severity: Important
Broken in: 3.14
Fixed in: 3.16



Subject: Wrong value from accessor while in :Init sub
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The attached test shows that the accessor to the field 'flag' in the Derived class does not return the correct value when called inside the '_init : Init' method in the Base class. In particular, I'm expecting the Derived->new(flag => 1) call to die, because the flag is set and this should trigger the die 'object is flagged!' if $self->is_flagged(); line in Base class initialisator. I tried to strip down the example to the very roots, bear with me if it's still not much clean. All the code is inside a single file, but it shows the same behaviour when I divide stuff into single files for test.pl, Base.pm and Derived.pm. I'm running perl v5.8.8 built for i686-linux. Regards, Flavio.
Subject: test.pl
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#!/usr/bin/perl use strict; use warnings; use Test::More 'no_plan'; use Test::Exception; throws_ok { Base->new(flag => 1) } qr/object\s+is\s+flagged!/mxsi, 'complains for flag set in Base class'; throws_ok { Derived->new() } qr/missing.*flag/mxsi, 'complains for missing parameter flag in Derived'; lives_ok { Derived->new(flag => 0) } 'lives with flag set to 0 in Derived'; my $object; throws_ok { $object = Derived->new(flag => 1) } qr/object\s+is\s+flagged!/mxsi, 'complains for flag set in Derived'; print 'object is ', ($object->is_flagged() ? '' : 'NOT '), "flagged\n"; BEGIN { package Base; { use strict; use warnings; use Object::InsideOut; sub _init : Init { my $self = shift; die 'object is flagged!' if $self->is_flagged(); return; } sub is_flagged { return 1; } } package Derived; { use strict; use warnings; use Object::InsideOut qw( Base ); my @flag : Field : Std(Name => 'flag', Private => 1) : Arg(Name => 'flag', Mandatory => 1); sub is_flagged { my $self = shift; return $self->get_flag(); } } } ## end BEGIN __END__ poletti@PolettiX:~/sviluppo/perl/Object-InsideOut$ perl test.pl ok 1 - complains for flag set in Base class ok 2 - complains for missing parameter flag in Derived ok 3 - lives with flag set to 0 in Derived not ok 4 - complains for flag set in Derived # Failed test 'complains for flag set in Derived' # at test.pl line 17. # expecting: Regexp ((?msix:object\s+is\s+flagged!)) # found: normal exit object is flagged 1..4 # Looks like you failed 1 test of 4.
From: JDHEDDEN [...] cpan.org
Show quoted text
> The attached test shows that the accessor to the field > 'flag' in the Derived class does not return the correct > value when called inside the '_init : Init' method in the > Base class. > > In particular, I'm expecting the > > Derived->new(flag => 1) > > call to die, because the flag is set and this should > trigger the > > die 'object is flagged!' if $self->is_flagged(); > > line in Base class initialisator.
Generally, object initialization proceeds from parent classes down through child classes. So, usually, it is a bad idea to call child class methods from the parent class before the object has been initialized in the child classes. I will change the object initialization process so that what you're trying to do will work, and I'll document the process in the POD. While not intended for such purposes, you can also accomplish what you're trying to do by adding a :PreInit subroutine to your child class: sub pre_init :PreInit { my ($self, $args) = @_; $flag[$$self] = $args->{'flag'}; } New version of OIO to follow shortly.
Subject: Re: [rt.cpan.org #27060] Wrong value from accessor while in :Init sub
Date: Fri, 11 May 2007 00:39:58 +0200 (CEST)
To: bug-Object-InsideOut [...] rt.cpan.org
From: "Flavio Poletti" <flavio [...] polettix.it>
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Show quoted text
> > <URL: http://rt.cpan.org/Ticket/Display.html?id=27060 > >
>> The attached test shows that the accessor to the field >> 'flag' in the Derived class does not return the correct >> value when called inside the '_init : Init' method in the >> Base class.
[snip] Show quoted text
> > Generally, object initialization proceeds from parent > classes down through child classes. So, usually, it is a > bad idea to call child class methods from the parent class > before the object has been initialized in the child classes.
This is probably the very reason why you can't count on inheritance when constructing objects in C++. But I noticed that the methods are already in place, and inheritance i honored... we're in Perl! So it sounded like this should work too. Show quoted text
> I will change the object initialization process so that what > you're trying to do will work, and I'll document the > process in the POD.
I tested your 3.16 version and it seems ok. Show quoted text
> While not intended for such purposes, you can also > accomplish what you're trying to do by adding a :PreInit > subroutine to your child class: > > sub pre_init :PreInit > { > my ($self, $args) = @_; > > $flag[$$self] = $args->{'flag'}; > } > > New version of OIO to follow shortly. >
I thought about using PreInit, but I was "blocked" by the docs that suggest not to set any variable when in PreInit. Now that I read your initialisation process description it makes perfect sense. I also hope that it isn't going to change, now that you put it into the docs :) Thanks, Flavio.


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