PerlX::Maybe(3pm) User Contributed Perl Documentation PerlX::Maybe(3pm)
NAME
PerlX::Maybe - return a pair only if they are both defined
SYNOPSIS
You 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,
);
DESCRIPTION
Moose 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) : (),
);
or:
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.
BUGS
Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=PerlX-Maybe <http://rt.cpan.org/Dist/Display.html?Queue=PerlX-Maybe>.
SEE ALSO
Syntax::Feature::Maybe.
MooseX::UndefTolerant, PerlX::Perform, Exporter.
AUTHOR
Toby Inkster <tobyink@cpan.org>.
COPYRIGHT AND LICENCE
This software is copyright (c) 2012 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 WARRANTIES
THIS 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.
perl v5.14.2 2012-05-03 PerlX::Maybe(3pm)