Paul Evans > Struct-Dumb > Struct::Dumb



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Struct::Dumb - make simple lightweight record-like structures


 use Struct::Dumb;
 struct Point => [qw( x y )];

 my $point = Point(10, 20);

 printf "Point is at (%d, %d)\n", $point->x, $point->y;

 $point->y = 30;
 printf "Point is now at (%d, %d)\n", $point->x, $point->y;

 struct Point3D => [qw( x y z )], named_constructor => 1;

 my $point3d = Point3D( z => 12, x => 100, y => 50 );

 printf "Point3d's height is %d\n", $point3d->z;

 struct Point3D => [qw( x y z )], predicate => "is_Point3D";

 my $point3d = Point3D( 1, 2, 3 );

 printf "This is a Point3D\n" if is_Point3D( $point3d );

 use Struct::Dumb qw( -named_constructors )

 struct Point3D => [qw( x y z ];

 my $point3d = Point3D( x => 100, z => 12, y => 50 );


Struct::Dumb creates record-like structure types, similar to the struct keyword in C, C++ or C#, or Record in Pascal. An invocation of this module will create a construction function which returns new object references with the given field values. These references all respond to lvalue methods that access or modify the values stored.

It's specifically and intentionally not meant to be an object class. You cannot subclass it. You cannot provide additional methods. You cannot apply roles or mixins or metaclasses or traits or antlers or whatever else is in fashion this week.

On the other hand, it is tiny, creates cheap lightweight array-backed structures, uses nothing outside of core. It's intended simply to be a slightly nicer way to store data structures, where otherwise you might be tempted to abuse a hash, complete with the risk of typoing key names. The constructor will croak if passed the wrong number of arguments, as will attempts to refer to fields that don't exist. Accessor-mutators will croak if invoked with extra arguments; a likely bug in case of mutations, or attempts to invoke a stored CODE reference.

 $ perl -E 'use Struct::Dumb; struct Point => [qw( x y )]; Point(30)'
 usage: main::Point($x, $y) at -e line 1

 $ perl -E 'use Struct::Dumb; struct Point => [qw( x y )]; Point(10,20)->z'
 main::Point does not have a 'z' field at -e line 1

 $ perl -E 'use Struct::Dumb; struct Point => [qw( x y )]; Point(1,2)->x(3)'
 main::Point->x invoked with arguments at -e line 1.


The struct and readonly_struct declarations create two different kinds of constructor function, depending on the setting of the named_constructor option. When false, the constructor takes positional values in the same order as the fields were declared. When true, the constructor takes a key/value pair list in no particular order, giving the value of each named field.

This option can be specified to the struct and readonly_struct functions. It defaults to false, but it can be set on a per-package basis to default true by supplying the -named_constructors option on the use statement.



   struct $name => [ @fieldnames ],
      named_constructor => (1|0),
      predicate         => "is_$name";

Creates a new structure type. This exports a new function of the type's name into the caller's namespace. Invoking this function returns a new instance of a type that implements those field names, as accessors and mutators for the fields.

Takes the following options:

named_constructor => BOOL

Determines whether the structure will take positional or named arguments.

predicate => STR

If defined, gives the name of a second function to export to the caller's namespace. This function will be a type test predicate; that is, a function that takes a single argmuent, and returns true if-and-only-if that argument is an instance of this structure type.


   readonly_struct $name => [ @fieldnames ],

Similar to "struct", but instances of this type are immutable once constructed. The field accessor methods will not be marked with the :lvalue attribute.

Takes the same options as "struct".



Paul Evans <>

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