oracular (3) Struct::Dumb.3pm.gz

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 optional

FUNCTIONS

   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_hash" option, giving name of another function to convert structs to
           key/value pairs, or a HASH ref.

AUTHOR

       Paul Evans <leonerd@leonerd.org.uk>