NAME
Variable::Strongly::Typed - Let some variables be strongly typed
VERSION
This document describes Variable::Strongly::Typed version 1.0.0
SYNOPSIS
use Variable::Strongly::Typed;
my $int :TYPE('int'); # must have an 'int' value
my $float :TYPE('float'); # must have a 'float' value
my $string :TYPE('string'); # must not be a reference
my $file :TYPE('IO::File'); # must be an IO::File
my @array_of_ints :TYPE('int'); # Each slot must contain
# an int
my %hash_of_floats :TYPE('float'); # Each value must be a float
my $int_own_error :TYPE('int', \&my_own_error_handler);
# Roll my own error handler
my @array_of_rgb :TYPE(\&red_green_blue); # my enumerated type
# For subs!!
sub return_an_int :TYPE('int') {
# .. do some stuff ..
return $something;
}
# ... and later ...
$int = 23; # All is well
$int = 'howdy!'; # This line will croak with a good error message
$float = 3.23; # All is well, nothing to see here
$float = new XML::Parser; # croak!
$array_of_ints[23] = 44; # Groovy
$array_of_ints[12] = 'yah'; # croak!
$hash_of_floats{pi} = 3.14159; # no problem
$hash_of_floats{e} = new IO::File; # croak!
# Return 1 if this val is RED, BLUE, or GREEN
# 0 otherwise
sub red_green_blue {
local $_ = shift;
/\A RED \z/xms || /\A BLUE \z/xms || /\A GREEN \z/xms;
}
$array_of_my_very_own_types[23] = 99; # croak!
$array_of_my_very_own_types[2] = 'BLUE'; # OK!
$int_own_error = 'lksdklwe'; # The sub 'my_own_error_hanlder'
# will be # called with the
# offending value
my $got_it = return_an_int(); # Will 'croak' (or call your error
# function) # if this sub doesn't
# return an 'int'DESCRIPTION
This modules allow you to strongly type your variables. Also known as the 'no fun' module - it can greatly enhance you code's quality and robustness.
By enforcing types on some (or all) of your variables you will eliminate a large class of careless (& not so careless) errors.
This could also aid an editor or code-browsing tools to verify code correctness without having to execute the script.
INTERFACE
Variable types are specified using the 'TYPE' attribute. There are currently 7 builtin types:
- 'int' => /\A \d+ \z/xms;
- 'string' => anything that's not a reference (!ref)
- 'float' => standard float regex
- 'bool' => same as 'int'
- 'SCALAR' => unblessed scalar ref
- 'ARRAY' => unblessed array ref
- 'HASH' => unblessed hash ref
You can also specify a class name like 'XML::Parser' - note this is NOT the same as 'HASH' which represents an unblessed HASH reference.
Note when specifying 'XML::Parser' assigning 'XML::Parser' or any subclass of 'XML::Parser' will be valid - it does a $value->isa('XML::Parser') (or whatever the type you specified was) to test the value.
If you try to assign an illegal value to your variable the assignment will croak with an informative error message. If you specify a second parameter in your 'TYPE' attribute it will be treated as a CODE ref to be called when the assignment will fail.
All builtin types allow 'undef' or any false value as a valid value. Your own types (see section below) should probably do the same.
ROLLING YOUR OWN TYPES
NOTE: You do NOT have to roll your own type to just specify a blessed object - see the section above!
Specifying a CODE ref in your TYPE() attribute allows you to define your own types. Your function will be call with 1 parameter - the value that's about to be assigned to any variable of that TYPE().
Returning 1 (or any true value) will allow the assignment to happen. Return 0 (or any false value) will cause to assignment to croak.
I'm sure you can dream up of all sorts of interesting types - enumerated types, all sorts of specific string types, bounded numbers, words only from a specific language are the sorts of things that pop into my mind. Again I heartily expect you to surprise me with the types you come up with.
Note also you must allow for 'undef' as that is the initial value your variable will have! Allowing for any false value may also be a good idea.
FUNCTION RETURN VALUES
By specifying a TYPE() attribute for a function you 'lock-down' that function to only return that type.
If your function returns an array every element of that array must be of the specified type.
ROLL YOUR OWN ERROR FUNCTION
By default Variable::Strongly::Typed croaks when an assignment fails. You can change this behavior by supplying a code ref as a second parameter in your TYPE() attribute.
If you do this, your function will be called instead of 'croak' with 1 parameter, the value to be assigned to the variable that failed.
If your function does not 'croak' or 'die' the assignment will occur so be careful!
DIAGNOSTICS
croak'ed error messages for built-in types look like:
Cannot assign <value> to a [ scalar | hash | array ]
of type <whatever>croak'ed error messages for user-supplied types look like:
Cannot assign <value> to a user-validated
[ scalar | hash | array ] variablecroak'ed error messages from an erroneous subroutine return value look like:
Cannot return <value> from a function or method of type
<whatever>If you'ved typed your subroutine & call it in a void context you'll get a croak like:
Throwing away return value of <whatever type it returns>CONFIGURATION AND ENVIRONMENT
Variable::Strongly::Typed requires no configuration files or environment variables.
DEPENDENCIES
Attribute::Handlers handle the attribute stuff Class::Std::Utils handle the basic 'inside-out' module work Test::More for testing version for versioning
INCOMPATIBILITIES
None reported.
BUGS AND LIMITATIONS
No bugs have been reported.
Please report any bugs or feature requests to bug-perl-strongly-typed@rt.cpan.org, or through the web interface at http://rt.cpan.org.
SEE ALSO
Attributes::Types - The main differences are you can type subroutines with this monster and you can specify a different error handler other than the default of 'croak'. Oh the code is a hella cleaner also. Other than that these two modules are very similar.
AUTHOR
Mark Ethan Trostler <mark@zzo.com>
LICENCE AND COPYRIGHT
Copyright (c) 2005, Mark Ethan Trostler <mark@zzo.com>. All rights reserved.
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.
DISCLAIMER OF WARRANTY
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