NAME
Struct::Dumb - make simple lightweight record-like structures
SYNOPSIS
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 );DESCRIPTION
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 arguments. (This helps detect likely bugs such as accidentally passing in the new value as an argument, or attempting to invoke a stored CODE reference by passing argument values directly to the accessor.)
$ 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.Objects in this class are (currently) backed by an ARRAY reference store, though this is an internal implementation detail and should not be relied on by using code. Attempting to dereference the object as an ARRAY will throw an exception.
Note: That on development perls that support use feature 'class', this is used instead of a blessed ARRAY reference. This implementation choice should be transparent to the end-user, as all the same features are supported.
CONSTRUCTOR FORMS
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.
When using named constructors, individual fields may be declared as being optional. By preceeding the field name with a ? character, the constructor is instructed not to complain if a named parameter is not given for that field; instead it will be set to undef.
struct Person => [qw( name age ?address )],
named_constructor => 1;
my $bob = Person( name => "Bob", age => 20 );
# This is valid because 'address' is marked as optionalFUNCTIONS
struct
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
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".
DATA::DUMP FILTER
Since version 0.10.
If Data::Dump is loaded, an extra filter is applied so that struct instances are printed in a format matching that which would construct them.
struct Colour => [qw( red green blue )];
use Data::Dump;
my %hash = ( col => Colour( 0.8, 0.5, 0.2 ) );
Data::Dump::dd \%hash;
# prints {col => main::Colour(0.8, 0.5, 0.2)}NOTES
Allowing ARRAY dereference
The way that forbidding access to instances as if they were ARRAY references is currently implemented uses an internal method on the generated structure class called _forbid_arrayification. If special circumstances require that this exception mechanism be bypassed, the method can be overloaded with an empty sub {} body, allowing the struct instances in that class to be accessed like normal ARRAY references. For good practice this should be limited by a local override.
For example, Devel::Cycle needs to access the instances as plain ARRAY references so it can walk the data structure looking for reference cycles.
use Devel::Cycle;
{
no warnings 'redefine';
local *Point::_forbid_arrayification = sub {};
memory_cycle_ok( $point );
}TODO
Consider adding an
coerce_hashoption, giving name of another function to convert structs to key/value pairs, or a HASH ref.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>