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 use PerlX::Maybe;
55 my $bob = Person->new(
57 (name => $name) x!!(defined $name),
58 (age => $age) x!!(defined $age),
59 );
60 A slightly more elegant solution is the "maybe" function.
62 Functions
64 "maybe $x => $y, @rest"
65 This function checks that $x and $y are both defined. If they are,
66 it returns them both as a list; otherwise it returns the empty
67 list.
68 If @rest is provided, it is unconditionally appended to the end of
70 whatever list is returned.
71 The combination of these behaviours allows the following very
73 sugary syntax to "just work".
74 my $bob = Person->new(
76 name => $name,
77 address => $addr,
78 maybe phone => $tel,
79 maybe email => $email,
80 unique_id => $id,
81 );
82 This function is exported by default.
84 "provided $condition, $x => $y, @rest"
86 Like "maybe" but allows you to use a custom condition expression:
87 my $bob = Person->new(
89 name => $name,
90 address => $addr,
91 provided length($tel), phone => $tel,
92 provided $email =~ /\@/, email => $email,
93 unique_id => $id,
94 );
95 This function is not exported by default.
97 "provided_deref $condition, $r, @rest"
99 Like "provided" but dereferences the second argument into list
100 context:
101 my $bob = Person->new(
103 name => $name,
104 address => $addr,
105 provided length($tel), phone => $tel,
106 provided $email =~ /\@/, email => $email,
107 provided_deref $employee, sub {
108 employee_id => $employee->employee_id,
109 maybe department => $employee->department,
110 },
111 unique_id => $id,
112 );
113 The second argument may be a HASH or ARRAY reference. It may also
115 be a CODE reference, which will be called in list context. If it is
116 a blessed object, it will be treated as if it were a HASH reference
117 (internally it could be another type of reference with
118 overloading). A code reference can be used if evaluation of the
119 second argument should only occur if the condition is met (e.g. to
120 prevent method calls on an uninitialised value).
121 This function is not exported by default.
123 "provided_deref_with_maybe $condition, $r, @rest"
125 Like "provide_deref" but will perform "maybe" on each key-value
126 pair in the dereferenced values.
127 my $bob = Person->new(
129 name => $name,
130 address => $addr,
131 provided length($tel), phone => $tel,
132 provided $email =~ /\@/, email => $email,
133 provided_deref_with_maybe $employee, $employee,
134 unique_id => $id,
135 );
136 Also, if the second argument is a blessed object, it will also skip
138 any 'private' attributes (keys starting with an underscore).
139 It not only "just works", it "DWIM"s!
141 This function is not exported by default.
143 "PerlX::Maybe::IMPLEMENTATION"
145 Indicates whether the XS backend PerlX::Maybe::XS was loaded.
146 XS Backend
148 If you install PerlX::Maybe::XS, a faster XS-based implementation will
149 be used instead of the pure Perl functions. My basic benchmarking
150 experiments seem to show this to be around 30% faster.
151 Currently there are no XS implementations of the "provided_deref" and
153 "provided_deref_with_maybe" functions. Contributions welcome.
154 Environment
156 The environment variable "PERLX_MAYBE_IMPLEMENTATION" may be set to
157 "PP" to prevent the XS backend from loading.
158 Exporting
160 Only "maybe" is exported by default. You can request other functions by
161 name:
162 use PerlX::Maybe "maybe", "provided";
164 Or to export everything:
166 use PerlX::Maybe ":all";
168 If Exporter::Tiny is installed, you can rename imports:
170 use PerlX::Maybe "maybe" => { -as => "perhaps" };
172
174 Please report any bugs to
175 <http://rt.cpan.org/Dist/Display.html?Queue=PerlX-Maybe>.
176
178 Syntax::Feature::Maybe, PerlX::Maybe::XS.
179 MooseX::UndefTolerant, PerlX::Perform, Exporter.
181
183 Toby Inkster <tobyink@cpan.org>.
184 "provided_deref" and "provided_deref_with_maybe" by Theo van Hoesel.
186
188 This software is copyright (c) 2012-2013, 2018 by Toby Inkster.
189 This is free software; you can redistribute it and/or modify it under
191 the same terms as the Perl 5 programming language system itself.
192
194 THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
195 WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
196 MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
197perl v5.30.0 2019-07-26 PerlX::Maybe(3)