SYNOPSISYou once wrote:
my $bob = Person->new(
defined $name ? (name => $name) : (),
defined $age ? (age => $age) : (),
Now you can write:
my $bob = Person->new( maybe name => $name, maybe age => $age, );
DESCRIPTIONMoose classes (and some other classes) distinguish between an attribute being unset and the attribute being set to undef. Supplying a constructor arguments like this:
my $bob = Person->new( name => $name, age => $age, );
Will result in the "name" and "age" attributes possibly being set to undef (if the corresponding $name and $age variables are not defined), which may violate the Person class' type constraints.
(Note: if you are the author of the class in question, you can solve this using MooseX::UndefTolerant. However, some of us are stuck using non-UndefTolerant classes written by third parties.)
To ensure that the Person constructor does not try to set a name or age at all when they are undefined, ugly looking code like this is often used:
my $bob = Person->new( defined $name ? (name => $name) : (), defined $age ? (age => $age) : (), );
my $bob = Person->new( (name => $name) x!!(defined $name), (age => $age) x!!(defined $age), );
A slightly more elegant solution is the "maybe" function.
- "maybe $x => $y, @rest"
This function checks that $x and $y are both defined. If they
are, it returns them both as a list; otherwise it returns the empty list.
If @rest is provided, it is unconditionally appended to the end of whatever list is returned.
The combination of these behaviours allows the following very sugary syntax to ``just work''.
my $bob = Person->new( name => $name, address => $addr, maybe phone => $tel, maybe email => $email, unique_id => $id, );
This function is exported by default.
- "provided $condition, $x => $y, @rest"
Like "maybe" but allows you to use a custom condition expression:
my $bob = Person->new( name => $name, address => $addr, provided length($tel), phone => $tel, provided $email =~ /\@/, email => $email, unique_id => $id, );
This function is not exported by default.
- Indicates whether the XS backend PerlX::Maybe::XS was loaded.
XS BackendIf you install PerlX::Maybe::XS, a faster XS-based implementation will be used instead of the pure Perl functions. My basic benchmarking experiments seem to show this to be around 30% faster.
EnvironmentThe environment variable "PERLX_MAYBE_IMPLEMENTATION" may be set to "PP" to prevent the XS backend from loading.
BUGSPlease report any bugs to <http://rt.cpan.org/Dist/Display.html?Queue=PerlX-Maybe>.
AUTHORToby Inkster <[email protected]>.
COPYRIGHT AND LICENCEThis software is copyright (c) 2012-2013 by Toby Inkster.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.
DISCLAIMER OF WARRANTIESTHIS PACKAGE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.