1PerlX::Maybe(3)       User Contributed Perl Documentation      PerlX::Maybe(3)
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NAME

6       PerlX::Maybe - return a pair only if they are both defined
7

SYNOPSIS

9       You once wrote:
10
11        my $bob = Person->new(
12           defined $name ? (name => $name) : (),
13           defined $age ? (age => $age) : (),
14        );
15
16       Now you can write:
17
18        my $bob = Person->new(
19           maybe name => $name,
20           maybe age  => $age,
21        );
22

DESCRIPTION

24       Moose classes (and some other classes) distinguish between an attribute
25       being unset and the attribute being set to undef. Supplying a
26       constructor arguments like this:
27
28        my $bob = Person->new(
29           name => $name,
30           age => $age,
31        );
32
33       Will result in the "name" and "age" attributes possibly being set to
34       undef (if the corresponding $name and $age variables are not defined),
35       which may violate the Person class' type constraints.
36
37       (Note: if you are the author of the class in question, you can solve
38       this using MooseX::UndefTolerant. However, some of us are stuck using
39       non-UndefTolerant classes written by third parties.)
40
41       To ensure that the Person constructor does not try to set a name or age
42       at all when they are undefined, ugly looking code like this is often
43       used:
44
45        my $bob = Person->new(
46           defined $name ? (name => $name) : (),
47           defined $age ? (age => $age) : (),
48        );
49
50       or:
51
52        my $bob = Person->new(
53           (name => $name) x!!(defined $name),
54           (age  => $age)  x!!(defined $age),
55        );
56
57       A slightly more elegant solution is the "maybe" function.
58
59   Functions
60       "maybe $x => $y, @rest"
61           This function checks that $x and $y are both defined. If they are,
62           it returns them both as a list; otherwise it returns the empty
63           list.
64
65           If @rest is provided, it is unconditionally appended to the end of
66           whatever list is returned.
67
68           The combination of these behaviours allows the following very
69           sugary syntax to "just work".
70
71            my $bob = Person->new(
72                    name      => $name,
73                    address   => $addr,
74              maybe phone     => $tel,
75              maybe email     => $email,
76                    unique_id => $id,
77            );
78
79           This function is exported by default.
80
81       "provided $condition, $x => $y, @rest"
82           Like "maybe" but allows you to use a custom condition expression:
83
84            my $bob = Person->new(
85                                        name      => $name,
86                                        address   => $addr,
87              provided length($tel),    phone     => $tel,
88              provided $email =~ /\@/,  email     => $email,
89                                        unique_id => $id,
90            );
91
92           This function is not exported by default.
93
94       "PerlX::Maybe::IMPLEMENTATION"
95           Indicates whether the XS backend PerlX::Maybe::XS was loaded.
96
97   XS Backend
98       If you install PerlX::Maybe::XS, a faster XS-based implementation will
99       be used instead of the pure Perl functions. My basic benchmarking
100       experiments seem to show this to be around 30% faster.
101
102   Environment
103       The environment variable "PERLX_MAYBE_IMPLEMENTATION" may be set to
104       "PP" to prevent the XS backend from loading.
105

BUGS

107       Please report any bugs to
108       <http://rt.cpan.org/Dist/Display.html?Queue=PerlX-Maybe>.
109

SEE ALSO

111       Syntax::Feature::Maybe, PerlX::Maybe::XS.
112
113       MooseX::UndefTolerant, PerlX::Perform, Exporter.
114

AUTHOR

116       Toby Inkster <tobyink@cpan.org>.
117

119       This software is copyright (c) 2012-2013 by Toby Inkster.
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121       This is free software; you can redistribute it and/or modify it under
122       the same terms as the Perl 5 programming language system itself.
123

DISCLAIMER OF WARRANTIES

125       THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
126       WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
127       MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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131perl v5.28.0                      2014-09-23                   PerlX::Maybe(3)
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