Attribute::Types
Attribute::Types
Attribute::Types - Attributes that confer type on variables
This document describes version 0.10 of Attribute::Types, released May 10, 2001.
use Attribute::Types;
my $count : INTEGER; # Can only store an integer
my $date : INTEGER(1..31); # Can only store an int between 1..31
my $value : NUMBER; # Can only store a number
my $score : NUMBER(0.1..9.9); # Can only store a num between 0.1..9.9
my @rain : NUMBER; # Elements can only store numbers
my %vars : SCALAR; # Entries can only store scalar refs
my %handler : CODE; # Entries can only store sub refs
my $arr : ARRAY; # Can only store array ref
my @hashes : HASH; # Elements can only store hash refs
my $glob : GLOB; # Can only store a typeglob ref
my $pattern : REGEX; # Can only store a qr'd regex
my $ref2 : REF; # Can only store a meta-reference
my $obj : Type(My::Class); # Can only store objects of (or
# derived from) the specified class
my $x : Type(/good|bad|ugly/); # Can only store strings matching
# the specified regex
sub odd { no warnings; $_[0]%2 }
my $guarded : Type(&odd); # Can only store values for which
# odd($value) returns true
$date = 23; # okay
$date = 32; # KABOOM!
$rain[1] = 121.7; # okay
$rain[1] = "lots"; # KABOOM!
$x = 'very good'; # okay
$x = 'excellent'; # KABOOM!
package My::Class::Der;
use base 'My::Class';
$obj = My::Class->new(); # okay
$obj = My::Class::Der->new(); # okay
$obj = Other::Class->new(); # KABOOM!
$guarded = 1; # okay
$guarded = 2; # KABOOM!
The Attribute::Types module provides 10 universally accessible attributes that can be used to create variables that accept assignments of only specific types of data.
The attributes are:
INTEGER
Indicates that the associated scalar, or the elements of the associated array,
or the entries of the associated hash can only contain integer values (those
values that are internally represented as actual numbers
(or may be converted to actual numbers without generating a warning),
and for which int($value)==$value).
The attribute may also be specified with a range of integer values, indicating a further restriction on the values the associated variable can store. For example:
my $x1 : INTEGER(1..100); # Any int between 1 and 100
my $x2 : INTEGER(-10..10); # Any ine between -10 and 10
my $x3 : INTEGER(0..); # Any positive int
my $x4 : INTEGER(..99); # Any int < 100 (including negatives)
NUMBER
Indicates that the associated scalar, or the elements of the associated array, or the entries of the associated hash can only contain values that are internally represented by (or silently convertible to) valid Perl numbers.
The attribute may also be specified with a range of numerical values, indicating a further restriction on the values the associated variable can store. For example:
my $x1 : NUMBER(1.0..100.0); # Any number between 1 and 100
my $x2 : NUMBER(-10..10); # Any number between -10 and 10
my $x3 : NUMBER(0..); # Any positive number
my $x4 : NUMBER(..99.9); # Any number < 99.9 (incl. negatives)
SCALAR
ref($value) eq 'SCALAR').
ARRAY
ref($value) eq 'ARRAY').
HASH
ref($value) eq 'HASH').
CODE
ref($value) eq 'CODE').
GLOB
ref($value) eq 'GLOB').
REF
ref($value) eq 'REF').
REGEX
ref($value) eq 'Regexp').
Type
Used to specify class-wise or generic storage constraints on a variable. There are three permitted syntaxes:
Type(Class::Name)
Type(/pattern/)
Type(&subname)
Indicates that the associated variable can only contain values for which the specified subroutine returns true when passed the value as its first argument.
Note that anonymous subroutines cannot be used in this context (they are run-time phenomena and types have to be set up at compile-time).
If the module is imported with a list of attribute names:
use Attribute::Types qw(INTEGER HASH);
then only those attributes can be used to specify types.
The type checking set up by this module is run-time type-checking. That is, the validity of an assignment is only checked when the assignment operation is actually performed, not when it is compiled.
Cannot assign value to type variable
Can't specify type attribute for CODE
Invalid type specifier: Type(garbage)
Type(...) attribute can only be specified with a class name, a
pattern (in /.../), or a subroutine name.
This is all Nat Torkington's idea.
Damian Conway (damian@conway.org)
There are undoubtedly serious bugs lurking somewhere in this code :-) Bug reports and other feedback are most welcome.
Copyright (c) 2001, Damian Conway. All Rights Reserved.
This module is free software. It may be used, redistributed
and/or modified under the same terms as Perl itself.