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.
Functions¶
- "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.
- "PerlX::Maybe::IMPLEMENTATION"
- Indicates whether the XS backend PerlX::Maybe::XS was loaded.
XS Backend¶
If 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.
Environment¶
The environment variable "PERLX_MAYBE_IMPLEMENTATION" may be set to
"PP" to prevent the XS backend from loading.
BUGS¶
Please report any bugs to
<
http://rt.cpan.org/Dist/Display.html?Queue=PerlX-Maybe>.
SEE ALSO¶
Syntax::Feature::Maybe, PerlX::Maybe::XS.
MooseX::UndefTolerant, PerlX::Perform, Exporter.
AUTHOR¶
Toby Inkster <tobyink@cpan.org>.
COPYRIGHT AND LICENCE¶
This 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 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.