1Struct::Dumb(3) User Contributed Perl Documentation Struct::Dumb(3)
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6 "Struct::Dumb" - make simple lightweight record-like structures
7
9 use Struct::Dumb;
10 struct Point => [qw( x y )];
12 my $point = Point(10, 20);
14 printf "Point is at (%d, %d)\n", $point->x, $point->y;
16 $point->y = 30;
18 printf "Point is now at (%d, %d)\n", $point->x, $point->y;
19 struct Point3D => [qw( x y z )], named_constructor => 1;
21 my $point3d = Point3D( z => 12, x => 100, y => 50 );
23 printf "Point3d's height is %d\n", $point3d->z;
25 struct Point3D => [qw( x y z )], predicate => "is_Point3D";
27 my $point3d = Point3D( 1, 2, 3 );
29 printf "This is a Point3D\n" if is_Point3D( $point3d );
31 use Struct::Dumb qw( -named_constructors )
33 struct Point3D => [qw( x y z )];
35 my $point3d = Point3D( x => 100, z => 12, y => 50 );
37
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 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 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 $ perl -E 'use Struct::Dumb; struct Point => [qw( x y )]; Point(30)'
62 usage: main::Point($x, $y) at -e line 1
63 $ 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 $ 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 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 Note: That on development perls that support "use feature 'class'",
76 this is used instead of a blessed ARRAY reference. This implementation
77 choice should be transparent to the end-user, as all the same features
78 are supported.
79 CONSTRUCTOR FORMS
81 The "struct" and "readonly_struct" declarations create two different
82 kinds of constructor function, depending on the setting of the
83 "named_constructor" option. When false, the constructor takes
84 positional values in the same order as the fields were declared. When
85 true, the constructor takes a key/value pair list in no particular
86 order, giving the value of each named field.
87 This option can be specified to the "struct" and "readonly_struct"
89 functions. It defaults to false, but it can be set on a per-package
90 basis to default true by supplying the "-named_constructors" option on
91 the "use" statement.
92 When using named constructors, individual fields may be declared as
94 being optional. By preceeding the field name with a "?" character, the
95 constructor is instructed not to complain if a named parameter is not
96 given for that field; instead it will be set to "undef".
97 struct Person => [qw( name age ?address )],
99 named_constructor => 1;
100 my $bob = Person( name => "Bob", age => 20 );
102 # This is valid because 'address' is marked as optional
103
105 struct
106 struct $name => [ @fieldnames ],
107 named_constructor => (1|0),
108 predicate => "is_$name";
109 Creates a new structure type. This exports a new function of the type's
111 name into the caller's namespace. Invoking this function returns a new
112 instance of a type that implements those field names, as accessors and
113 mutators for the fields.
114 Takes the following options:
116 named_constructor => BOOL
118 Determines whether the structure will take positional or named
119 arguments.
120 predicate => STR
122 If defined, gives the name of a second function to export to the
123 caller's namespace. This function will be a type test predicate;
124 that is, a function that takes a single argmuent, and returns true
125 if-and-only-if that argument is an instance of this structure type.
126 readonly_struct
128 readonly_struct $name => [ @fieldnames ],
129 ...
130 Similar to "struct", but instances of this type are immutable once
132 constructed. The field accessor methods will not be marked with the
133 ":lvalue" attribute.
134 Takes the same options as "struct".
136
138 Since version 0.10.
139 If Data::Dump is loaded, an extra filter is applied so that struct
141 instances are printed in a format matching that which would construct
142 them.
143 struct Colour => [qw( red green blue )];
145 use Data::Dump;
147 my %hash = ( col => Colour( 0.8, 0.5, 0.2 ) );
149 Data::Dump::dd \%hash;
150 # prints {col => main::Colour(0.8, 0.5, 0.2)}
152
154 Allowing ARRAY dereference
155 The way that forbidding access to instances as if they were ARRAY
156 references is currently implemented uses an internal method on the
157 generated structure class called "_forbid_arrayification". If special
158 circumstances require that this exception mechanism be bypassed, the
159 method can be overloaded with an empty "sub {}" body, allowing the
160 struct instances in that class to be accessed like normal ARRAY
161 references. For good practice this should be limited by a "local"
162 override.
163 For example, Devel::Cycle needs to access the instances as plain ARRAY
165 references so it can walk the data structure looking for reference
166 cycles.
167 use Devel::Cycle;
169 {
171 no warnings 'redefine';
172 local *Point::_forbid_arrayification = sub {};
173 memory_cycle_ok( $point );
175 }
176
178 • Consider adding an "coerce_hash" option, giving name of another
179 function to convert structs to key/value pairs, or a HASH ref.
180
182 Paul Evans <leonerd@leonerd.org.uk>
183perl v5.36.0 2023-01-20 Struct::Dumb(3)