1PerlX::Maybe(3) User Contributed Perl Documentation PerlX::Maybe(3)
2
6 PerlX::Maybe - return a pair only if they are both defined
7
9 You once wrote:
10 my $bob = Person->new(
12 defined $name ? (name => $name) : (),
13 defined $age ? (age => $age) : (),
14 );
15 Now you can write:
17 use PerlX::Maybe;
19 my $bob = Person->new(
21 maybe name => $name,
22 maybe age => $age,
23 );
24
26 Moose classes (and some other classes) distinguish between an attribute
27 being unset and the attribute being set to undef. Supplying a
28 constructor arguments like this:
29 my $bob = Person->new(
31 name => $name,
32 age => $age,
33 );
34 Will result in the "name" and "age" attributes possibly being set to
36 undef (if the corresponding $name and $age variables are not defined),
37 which may violate the Person class' type constraints.
38 (Note: if you are the author of the class in question, you can solve
40 this using MooseX::UndefTolerant. However, some of us are stuck using
41 non-UndefTolerant classes written by third parties.)
42 To ensure that the Person constructor does not try to set a name or age
44 at all when they are undefined, ugly looking code like this is often
45 used:
46 my $bob = Person->new(
48 defined $name ? (name => $name) : (),
49 defined $age ? (age => $age) : (),
50 );
51 or:
53 my $bob = Person->new(
55 (name => $name) x!!(defined $name),
56 (age => $age) x!!(defined $age),
57 );
58 A slightly more elegant solution is the "maybe" function.
60 Functions
62 "maybe $x => $y, @rest"
63 This function checks that $x and $y are both defined. If they are,
64 it returns them both as a list; otherwise it returns the empty
65 list.
66 If @rest is provided, it is unconditionally appended to the end of
68 whatever list is returned.
69 The combination of these behaviours allows the following very
71 sugary syntax to "just work".
72 my $bob = Person->new(
74 name => $name,
75 address => $addr,
76 maybe phone => $tel,
77 maybe email => $email,
78 unique_id => $id,
79 );
80 This function is exported by default.
82 "provided $condition, $x => $y, @rest"
84 Like "maybe" but allows you to use a custom condition expression:
85 my $bob = Person->new(
87 name => $name,
88 address => $addr,
89 provided length($tel), phone => $tel,
90 provided $email =~ /\@/, email => $email,
91 unique_id => $id,
92 );
93 This function is not exported by default.
95 "provided_deref $condition, $r, @rest"
97 Like "provided" but dereferences the second argument into list
98 context:
99 my $bob = Person->new(
101 name => $name,
102 address => $addr,
103 provided length($tel), phone => $tel,
104 provided $email =~ /\@/, email => $email,
105 provided_deref $employee, sub {
106 employee_id => $employee->employee_id,
107 maybe department => $employee->department,
108 },
109 unique_id => $id,
110 );
111 The second argument may be a HASH or ARRAY reference. It may also
113 be a CODE reference, which will be called in list context. If it is
114 a blessed object, it will be treated as if it were a HASH reference
115 (internally it could be another type of reference with
116 overloading). A code reference can be used if evaluation of the
117 second argument should only occur if the condition is met (e.g. to
118 prevent method calls on an uninitialised value).
119 This function is not exported by default.
121 "provided_deref_with_maybe $condition, $r, @rest"
123 Like "provide_deref" but will perform "maybe" on each key-value
124 pair in the dereferenced values.
125 my $bob = Person->new(
127 name => $name,
128 address => $addr,
129 provided length($tel), phone => $tel,
130 provided $email =~ /\@/, email => $email,
131 provided_deref_with_maybe $employee, $employee,
132 unique_id => $id,
133 );
134 Also, if the second argument is a blessed object, it will also skip
136 any 'private' attributes (keys starting with an underscore).
137 It not only "just works", it "DWIM"s!
139 This function is not exported by default.
141 "PerlX::Maybe::IMPLEMENTATION"
143 Indicates whether the XS backend PerlX::Maybe::XS was loaded.
144 XS Backend
146 If you install PerlX::Maybe::XS, a faster XS-based implementation will
147 be used instead of the pure Perl functions. My basic benchmarking
148 experiments seem to show this to be around 30% faster.
149 Currently there are no XS implementations of the "provided_deref" and
151 "provided_deref_with_maybe" functions. Contributions welcome.
152 Environment
154 The environment variable "PERLX_MAYBE_IMPLEMENTATION" may be set to
155 "PP" to prevent the XS backend from loading.
156 Exporting
158 Only "maybe" is exported by default. You can request other functions by
159 name:
160 use PerlX::Maybe "maybe", "provided";
162 Or to export everything:
164 use PerlX::Maybe ":all";
166 If Exporter::Tiny is installed, you can rename imports:
168 use PerlX::Maybe "maybe" => { -as => "perhaps" };
170
172 Please report any bugs to
173 <http://rt.cpan.org/Dist/Display.html?Queue=PerlX-Maybe>.
174
176 Syntax::Feature::Maybe, PerlX::Maybe::XS.
177 MooseX::UndefTolerant, PerlX::Perform, Exporter.
179
181 Toby Inkster <tobyink@cpan.org>.
182 "provided_deref" and "provided_deref_with_maybe" by Theo van Hoesel.
184
186 This software is copyright (c) 2012-2013, 2018 by Toby Inkster.
187 This is free software; you can redistribute it and/or modify it under
189 the same terms as the Perl 5 programming language system itself.
190
192 THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
193 WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
194 MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
195perl v5.36.0 2023-01-20 PerlX::Maybe(3)