1Struct::Dumb(3)       User Contributed Perl Documentation      Struct::Dumb(3)
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4

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 );
37

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

FUNCTIONS

89   struct
90          struct $name => [ @fieldnames ],
91             named_constructor => (1|0),
92             predicate         => "is_$name";
93
94       Creates a new structure type. This exports a new function of the type's
95       name into the caller's namespace. Invoking this function returns a new
96       instance of a type that implements those field names, as accessors and
97       mutators for the fields.
98
99       Takes the following options:
100
101       named_constructor => BOOL
102           Determines whether the structure will take positional or named
103           arguments.
104
105       predicate => STR
106           If defined, gives the name of a second function to export to the
107           caller's namespace. This function will be a type test predicate;
108           that is, a function that takes a single argmuent, and returns true
109           if-and-only-if that argument is an instance of this structure type.
110
111   readonly_struct
112          readonly_struct $name => [ @fieldnames ],
113             ...
114
115       Similar to "struct", but instances of this type are immutable once
116       constructed. The field accessor methods will not be marked with the
117       ":lvalue" attribute.
118
119       Takes the same options as "struct".
120

NOTES

122   Allowing ARRAY dereference
123       The way that forbidding access to instances as if they were ARRAY
124       references is currently implemented uses an internal method on the
125       generated structure class called "_forbid_arrayification". If special
126       circumstances require that this exception mechanism be bypassed, the
127       method can be overloaded with an empty "sub {}" body, allowing the
128       struct instances in that class to be accessed like normal ARRAY
129       references. For good practice this should be limited by a "local"
130       override.
131
132       For example, Devel::Cycle needs to access the instances as plain ARRAY
133       references so it can walk the data structure looking for reference
134       cycles.
135
136        use Devel::Cycle;
137
138        {
139           no warnings 'redefine';
140           local *Point::_forbid_arrayification = sub {};
141
142           memory_cycle_ok( $point );
143        }
144

TODO

146       ยท   Consider adding an "coerce_hash" option, giving name of another
147           function to convert structs to key/value pairs, or a HASH ref.
148

AUTHOR

150       Paul Evans <leonerd@leonerd.org.uk>
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154perl v5.28.1                      2019-02-02                   Struct::Dumb(3)
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