1Struct::Dumb(3)       User Contributed Perl Documentation      Struct::Dumb(3)
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NAME

6       "Struct::Dumb" - make simple lightweight record-like structures
7

SYNOPSIS

9        use Struct::Dumb;
10
11        struct Point => [qw( x y )];
12
13        my $point = Point(10, 20);
14
15        printf "Point is at (%d, %d)\n", $point->x, $point->y;
16
17        $point->y = 30;
18        printf "Point is now at (%d, %d)\n", $point->x, $point->y;
19
20        struct Point3D => [qw( x y z )], named_constructor => 1;
21
22        my $point3d = Point3D( z => 12, x => 100, y => 50 );
23
24        printf "Point3d's height is %d\n", $point3d->z;
25
26        struct Point3D => [qw( x y z )], predicate => "is_Point3D";
27
28        my $point3d = Point3D( 1, 2, 3 );
29
30        printf "This is a Point3D\n" if is_Point3D( $point3d );
31
32        use Struct::Dumb qw( -named_constructors )
33
34        struct Point3D => [qw( x y z )];
35
36        my $point3d = Point3D( x => 100, z => 12, y => 50 );
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DESCRIPTION

39       "Struct::Dumb" creates record-like structure types, similar to the
40       "struct" keyword in C, C++ or C#, or "Record" in Pascal. An invocation
41       of this module will create a construction function which returns new
42       object references with the given field values. These references all
43       respond to lvalue methods that access or modify the values stored.
44
45       It's specifically and intentionally not meant to be an object class.
46       You cannot subclass it. You cannot provide additional methods. You
47       cannot apply roles or mixins or metaclasses or traits or antlers or
48       whatever else is in fashion this week.
49
50       On the other hand, it is tiny, creates cheap lightweight array-backed
51       structures, uses nothing outside of core. It's intended simply to be a
52       slightly nicer way to store data structures, where otherwise you might
53       be tempted to abuse a hash, complete with the risk of typoing key
54       names. The constructor will "croak" if passed the wrong number of
55       arguments, as will attempts to refer to fields that don't exist.
56       Accessor-mutators will "croak" if invoked with arguments. (This helps
57       detect likely bugs such as accidentally passing in the new value as an
58       argument, or attempting to invoke a stored "CODE" reference by passing
59       argument values directly to the accessor.)
60
61        $ perl -E 'use Struct::Dumb; struct Point => [qw( x y )]; Point(30)'
62        usage: main::Point($x, $y) at -e line 1
63
64        $ perl -E 'use Struct::Dumb; struct Point => [qw( x y )]; Point(10,20)->z'
65        main::Point does not have a 'z' field at -e line 1
66
67        $ perl -E 'use Struct::Dumb; struct Point => [qw( x y )]; Point(1,2)->x(3)'
68        main::Point->x invoked with arguments at -e line 1.
69
70       Objects in this class are (currently) backed by an ARRAY reference
71       store, though this is an internal implementation detail and should not
72       be relied on by using code. Attempting to dereference the object as an
73       ARRAY will throw an exception.
74
75   CONSTRUCTOR FORMS
76       The "struct" and "readonly_struct" declarations create two different
77       kinds of constructor function, depending on the setting of the
78       "named_constructor" option. When false, the constructor takes
79       positional values in the same order as the fields were declared. When
80       true, the constructor takes a key/value pair list in no particular
81       order, giving the value of each named field.
82
83       This option can be specified to the "struct" and "readonly_struct"
84       functions. It defaults to false, but it can be set on a per-package
85       basis to default true by supplying the "-named_constructors" option on
86       the "use" statement.
87
88       When using named constructors, individual fields may be declared as
89       being optional. By preceeding the field name with a "?" character, the
90       constructor is instructed not to complain if a named parameter is not
91       given for that field; instead it will be set to "undef".
92
93          struct Person => [qw( name age ?address )],
94             named_constructor => 1;
95
96          my $bob = Person( name => "Bob", age => 20 );
97          # This is valid because 'address' is marked as optional
98

FUNCTIONS

100   struct
101          struct $name => [ @fieldnames ],
102             named_constructor => (1|0),
103             predicate         => "is_$name";
104
105       Creates a new structure type. This exports a new function of the type's
106       name into the caller's namespace. Invoking this function returns a new
107       instance of a type that implements those field names, as accessors and
108       mutators for the fields.
109
110       Takes the following options:
111
112       named_constructor => BOOL
113           Determines whether the structure will take positional or named
114           arguments.
115
116       predicate => STR
117           If defined, gives the name of a second function to export to the
118           caller's namespace. This function will be a type test predicate;
119           that is, a function that takes a single argmuent, and returns true
120           if-and-only-if that argument is an instance of this structure type.
121
122   readonly_struct
123          readonly_struct $name => [ @fieldnames ],
124             ...
125
126       Similar to "struct", but instances of this type are immutable once
127       constructed. The field accessor methods will not be marked with the
128       ":lvalue" attribute.
129
130       Takes the same options as "struct".
131

DATA::DUMP FILTER

133       Since version 0.10.
134
135       If Data::Dump is loaded, an extra filter is applied so that struct
136       instances are printed in a format matching that which would construct
137       them.
138
139          struct Colour => [qw( red green blue )];
140
141          use Data::Dump;
142
143          my %hash = ( col => Colour( 0.8, 0.5, 0.2 ) );
144          Data::Dump::dd \%hash;
145
146          # prints {col => main::Colour(0.8, 0.5, 0.2)}
147

NOTES

149   Allowing ARRAY dereference
150       The way that forbidding access to instances as if they were ARRAY
151       references is currently implemented uses an internal method on the
152       generated structure class called "_forbid_arrayification". If special
153       circumstances require that this exception mechanism be bypassed, the
154       method can be overloaded with an empty "sub {}" body, allowing the
155       struct instances in that class to be accessed like normal ARRAY
156       references. For good practice this should be limited by a "local"
157       override.
158
159       For example, Devel::Cycle needs to access the instances as plain ARRAY
160       references so it can walk the data structure looking for reference
161       cycles.
162
163        use Devel::Cycle;
164
165        {
166           no warnings 'redefine';
167           local *Point::_forbid_arrayification = sub {};
168
169           memory_cycle_ok( $point );
170        }
171

TODO

173       •   Consider adding an "coerce_hash" option, giving name of another
174           function to convert structs to key/value pairs, or a HASH ref.
175

AUTHOR

177       Paul Evans <leonerd@leonerd.org.uk>
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181perl v5.36.0                      2022-07-22                   Struct::Dumb(3)
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