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.