Re: attribute w/ coerce and trigger - trigger arguments

Charles,

You have indeed found a bug, using the accessor directly behaves  
correctly, but using the constructor does not behave correctly. I am  
busy with work stuff right now, but I will fix this ASAP and it will  
be in the next release.

- Stevan


On Apr 9, 2008, at 2:40 PM, Charles Alderman wrote:
> Hello,
>
> Just started using Moose (love it).  I recently spent a little time  
> struggling through an issue with trigger arguments for a coerced  
> attribute.  So, I thought I'd post what I found here in case anyone  
> else runs into it.
>
> Actually, I'm not sure if I found an undocumented feature of Moose,  
> or if it's a bug.  The docs say that a trigger is passed an updated  
> value of the attribute.  What happens is that if the attribute has  
> a coercion, the argument passed to the trigger hasn't been  
> coerced.  So, technically, the argument isn't an updated value.   
> (At least, that's where my confusion came from.)
>
> The coerced value is still available to the trigger through the  
> attribute's accessor, so maybe having the non-coerced value also  
> available is for the best.
>
> For clarification, I included an example.
>
> Thanks,
> Charles Alderman
> aldermania.com
>
> Versions:
> Moose - 0.40
> Class::MOP - 0.54
>
> --
>
> From the Moose perldoc:
>
> The trigger option is a CODE reference which will be called after  
> the value of the attribute is set. The CODE ref will be passed the  
> instance itself, the **updated value** and the attribute meta- 
> object (this is for more advanced fiddling and can typically be  
> ignored).
>
> --
>
> Here's an example:
> #This example is based on: Schwartz, R.L. "The Moose is Flying  
> (part 2)". LinuxMag Column 95 (Jul 2007)
>
> package Mortgage;
>
> use Moose;
> use Moose::Util::TypeConstraints;
>
> use DateTime;
> use DateTime::Format::DateManip;
> use Date::Manip;
> Date_Init( 'TZ=US/Eastern' );
>
> subtype 'DateTime'
>   => as 'Object'
>   => where { $_->isa('DateTime') };
>
> coerce 'DateTime'
>   => from 'Str'     => via { DateTime::Format::DateManip- 
> >parse_datetime($_) }
>   => from 'HashRef' => via { DateTime->new(%$_) };
>
> has 'closing_date' => (
>   is => 'rw',
>   isa => 'DateTime',
>   coerce => 1,
>
>   trigger => sub {
>     my ( $self, $val, $meta ) = @_;
>     print $self->closing_date->isa('DateTime') ? 'yes' : 'no';  # yes
>     print $val->isa('DateTime')                ? 'yes' : 'no';  #  
> no???
>   }
> );
>
> 1;
>
> package main;
>
> my $mtg = Mortgage->new( closing_date => 'yesterday' );
> print $mtg->closing_date->isa('DateTime') ? 'yes' : 'no';  # yes
>
>