Type::Coercion on the fly

jandrew has asked for the wisdom of the Perl Monks concerning the following question:

Hello all,

I have one of those questions where the possible answer may be don't do that. However, I am attempting to build Type::Coercion objects/instances on the fly and I am having some trouble figuring out what I'm doing wrong.

I would like the code below;

#! perl
use strict;
use warnings;
use Type::Utils -all;
use Type::Library
    -base,
    -declare => qw( IncreaseMagnetude );
use Types::Standard qw( Num Str );
use Type::Coercion;

my $lookup ={ Ten => 10 };

declare_coercion IncreaseMagnetude,
    to_type Num,
    from Str,
    via{ $lookup->{$_} * 10 };

# Alternate on-the-fly version
my  $more_magnetude = Type::Coercion->new(
        name    => 'MoreMagnitude',
        to_type => Num,
        from    => Str,
        via     => sub{ $lookup->{$_}* 11 },
    );

print "Using: " . IncreaseMagnetude->display_name . " -> ";
print IncreaseMagnetude->( 'Ten' ) . "\n";
print "Using: " . $more_magnetude->display_name . " -> ";
print $more_magnetude->( 'Ten' ) . "\n";
[download]

to print out the following;

Using: IncreaseMagnetude -> 100
Using: MoreMagnitude -> 110
[download]

but instead I get;

Using: IncreaseMagnetude -> 100
Using: MoreMagnitude -> Ten
[download]

Comment on Type::Coercion on the fly Select or Download Code

Replies are listed 'Best First'.
Re: Type::Coercion on the fly by tobyink (Canon) on Jul 08, 2014 at 15:36 UTC
Try it like this: `my $more_magnetude = Type::Coercion->new( name => 'MoreMagnitude', type_constraint => Num, type_coercion_map => [ Str, sub { $lookup->{$_}* 11 } ], );` [download] See the documentation of the constructor and attributes of Type::Coercion. (If it makes you feel any better, it took me a several minutes to spot what you were going wrong.) toby döt ink	[reply] [d/l]
Re^2: Type::Coercion on the fly by jandrew (Chaplain) on Jul 08, 2014 at 16:08 UTC
tobyink++ That was both fast and helpful! Thanks for the solution and the pointer to the documentation. Update: I'm looking forward to the book!	[reply]