1Return::Type(3)       User Contributed Perl Documentation      Return::Type(3)
2
3
4

NAME

6       Return::Type - specify a return type for a function (optionally with
7       coercion)
8

SYNOPSIS

10          use Return::Type;
11          use Types::Standard qw(Int);
12
13          sub first_item :ReturnType(Int) {
14             return $_[0];
15          }
16
17          my $answer = first_item(42, 43, 44);     # returns 42
18          my $pie    = first_item(3.141592);       # throws an error!
19

DESCRIPTION

21       Return::Type allows you to specify a return type for your subs. Type
22       constraints from any Type::Tiny, MooseX::Types or MouseX::Types type
23       library are supported.
24
25       The simple syntax for specifying a type constraint is shown in the
26       "SYNOPSIS". If the attribute is passed a single type constraint as
27       shown, this will be applied to the return value if called in scalar
28       context, and to each item in the returned list if called in list
29       context. (If the sub is called in void context, type constraints are
30       simply ignored.)
31
32       It is possible to specify different type constraints for scalar and
33       list context:
34
35          sub foo :ReturnType(scalar => Int, list => HashRef[Num]) {
36             if (wantarray) {
37                return (pie => 3.141592);
38             }
39             else {
40                return 42;
41             }
42          }
43
44       The return value is not type checked if the function is called in void
45       context.
46
47          # Note that the ~Any type is the opposite of Any.
48          # So all values will fail the type check.
49          # That means that the following function can only
50          # be called in void context.
51          #
52          sub foo :ReturnType(scalar => ~Any, list => ~Any) {
53             ...;
54          }
55
56          # Shortcut for the above.
57          #
58          sub foo :ReturnType(Void) {
59             ...;
60          }
61
62       Note that because type constraint libraries are really aimed at
63       validating scalars, the type constraint for the list is specified as a
64       hashref of numbers and not a hash of numbers! For the purposes of
65       validation against the type constraint, we slurp the returned list into
66       a temporary arrayref or hashref.
67
68       For type constraints with coercions, you can also pass the option
69       "coerce => 1":
70
71          use Return::Type;
72          use Types::Standard qw( Int Num );
73
74          # Define a subtype of "Int" at compile time, which can
75          # coerce from "Num" by rounding to nearest integer.
76          use constant Rounded => Int->plus_coercions(Num, sub { int($_) });
77
78          sub first_item :ReturnType(scalar => Rounded, coerce => 1) {
79             return $_[0];
80          }
81
82          my $answer = first_item(42, 43, 44);     # returns 42
83          my $pie    = first_item(3.141592);       # returns 3
84
85       The options "coerce_scalar" and "coerce_list" are also available if you
86       wish to enable coercion only in particular contexts.
87
88   Power-user Inferface
89       Rather than using the ":ReturnType" attribute, it's possible to wrap a
90       coderef like this:
91
92          my $wrapped = Return::Type->wrap_sub($orig, %options);
93
94       The accepted options are "scalar", "list", "coerce", "coerce_list", and
95       "coerce_scalar", as per the attribute-based interface.
96
97       There is an additional option "scope_upper" which will load and use
98       Scope::Upper so that things like "caller" used within the wrapped sub
99       are unaware of being wrapped. This behaviour was the default prior to
100       Return::Type 0.004, but is now optional and disabled by default.
101

BUGS

103       Please report any bugs to
104       <http://rt.cpan.org/Dist/Display.html?Queue=Return-Type>.
105

SUPPORT

107       IRC: support is available through in the #moops channel on irc.perl.org
108       <http://www.irc.perl.org/channels.html>.
109

SEE ALSO

111       Attribute::Contract, Sub::Filter, Sub::Contract.
112

AUTHOR

114       Toby Inkster <tobyink@cpan.org>.
115

117       This software is copyright (c) 2013-2014 by Toby Inkster.
118
119       This is free software; you can redistribute it and/or modify it under
120       the same terms as the Perl 5 programming language system itself.
121

DISCLAIMER OF WARRANTIES

123       THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
124       WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
125       MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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129perl v5.34.0                      2021-07-22                   Return::Type(3)
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