Types-Serialiser/Serialiser.pm

=head1 NAME

Types::Serialiser - simple data types for common serialisation formats

=encoding utf-8

=head1 SYNOPSIS

=head1 DESCRIPTION

This module provides some extra datatypes that are used by common
serialisation formats such as JSON or CBOR. The idea is to have a
repository of simple/small constants and containers that can be shared by
different implementations so they become interoperable between each other.

=cut

package Types::Serialiser;

our $VERSION = 0.01;

=head1 SIMPLE SCALAR CONSTANTS

Simple scalar constants are values that are overloaded to act like simple
Perl values, but have (class) type to differentiate them from normal Perl
scalars. This is necessary because these have different representations in
the serialisation formats.

=head2 BOOLEANS (Types::Serialiser::Boolean class)

This type has only two instances, true and false. A natural representation
for these in Perl is C<1> and C<0>, but serialisation formats need to be
able to differentiate between them and mere numbers.

=over 4

=item $Types::Serialiser::true, Types::Serialiser::true

This value represents the "true" value. In most contexts is acts like
the number C<1>. It is up to you whether you use the variable form
(C<$Types::Serialiser::true>) or the constant form (C<Types::Serialiser::true>).

The constant is represented as a reference to a scalar containing C<1> -
implementations are allowed to directly test for this.

=item $Types::Serialiser::false, Types::Serialiser::false

This value represents the "false" value. In most contexts is acts like
the number C<0>. It is up to you whether you use the variable form
(C<$Types::Serialiser::false>) or the constant form (C<Types::Serialiser::false>).

The constant is represented as a reference to a scalar containing C<0> -
implementations are allowed to directly test for this.

=item $is_bool = Types::Serialiser::is_bool $value

Returns true iff the C<$value> is either C<$Types::Serialiser::true> or
C<$Types::Serialiser::false>.

For example, you could differentiate between a perl true value and a
C<Types::Serialiser::true> by using this:

   $value && Types::Serialiser::is_bool $value

=item $is_true = Types::Serialiser::is_true $value

Returns true iff C<$value> is C<$Types::Serialiser::true>.

=item $is_false = Types::Serialiser::is_false $value

Returns false iff C<$value> is C<$Types::Serialiser::false>.

=back

=head2 ERROR (Types::Serialiser::Error class)

This class has only a single instance, C<error>. It is used to signal
an encoding or decoding error. In CBOR for example, and object that
couldn't be encoded will be represented by a CBOR undefined value, which
is represented by the error value in Perl.

=over 4

=item $Types::Serialiser::error, Types::Serialiser::error

This value represents the "error" value. Accessing values of this type
will throw an exception.

The constant is represented as a reference to a scalar containing C<undef>
- implementations are allowed to directly test for this.

=item $is_error = Types::Serialiser::is_error $value

Returns false iff C<$value> is C<$Types::Serialiser::error>.

=back

=cut

our $true  = do { bless \(my $dummy = 1), Types::Serialiser::Boolean:: };
our $false = do { bless \(my $dummy = 0), Types::Serialiser::Boolean:: };
our $error = do { bless \(my $dummy    ), Types::Serialiser::Error::   };

sub true  () { $true  }
sub false () { $false }
sub error () { $error }

sub is_bool  ($) {           UNIVERSAL::isa $_[0], Types::Serialiser::Boolean:: }
sub is_true  ($) {  $_[0] && UNIVERSAL::isa $_[0], Types::Serialiser::Boolean:: }
sub is_false ($) { !$_[0] && UNIVERSAL::isa $_[0], Types::Serialiser::Boolean:: }
sub is_error ($) {           UNIVERSAL::isa $_[0], Types::Serialiser::Error::   }

package Types::Serialiser::Boolean;

use overload
   "0+"     => sub { ${$_[0]} },
   "++"     => sub { $_[0] = ${$_[0]} + 1 },
   "--"     => sub { $_[0] = ${$_[0]} - 1 },
   fallback => 1;

package Types::Serialiser::Error;

sub error {
   require Carp;
   Carp::croak ("caught attempt to use the Types::Serialiser::error value");
};

use overload
   "0+"     => \&error,
   "++"     => \&error,
   "--"     => \&error,
   fallback => 1;

=head1 NOTES FOR XS USERS

The recommended way to detect whether a scalar is one of these objects
is to check whether the stash is the C<Types::Serialiser::Boolean> or
C<Types::Serialiser::Error> stash, and then follow the scalar reference to
see if it's C<1> (true), C<0> (false) or C<undef> (error).

While it is possible to use an isa test, directly comparing stash pointers
is faster and guaranteed to work.

=head1 A GENERIC OBJECT SERIALIATION PROTOCOL

This section explains the object serialisation protocol used by
L<CBOR::XS>. It is meant to be generic enough to support any kind of
generic object serialiser.

This protocol is called "the Types::Serialiser object serialisation
protocol".

=head2 ENCODING

When the encoder encounters an object that it cannot otherwise encode (for
example, L<CBOR::XS> can encode a few special types itself, and will first
attempt to use the special C<TO_CBOR> serialisation protocol), it will
look up the C<FREEZE> method on the object.

If it exists, it will call it with two arguments: the object to
serialise, and a constant string that indicates the name of the
serialisationformat. For example L<CBOR::XS> uses C<CBOR>, and L<JSON> and
L<JSON::XS> (or any other JSON serialiser), would use C<JSON> as second
argument.

The C<FREEZE> method can then return zero or more values to identify the
object instance. The serialiser is then supposed to encode the class name
and all of these return values (which must be encodable in the format)
using the relevant form for perl objects. In CBOR for example, there is a
registered tag number for encoded perl objects.

=head2 DECODING

When the decoder then encounters such an encoded perl object, it should
look up the C<THAW> method on the stored classname, and invoke it with the
classname, the constant string to identify the format, and all the return
values returned by C<FREEZE>.

=head2 EXAMPLES

See the C<OBJECT SERIALISATION> section in the L<CBOR::XS> manpage for
more details, an example implementation, and code examples.

Here is an example C<FREEZE>/C<THAW> method pair:

   sub My::Object::FREEZE {
      my ($self, $serialiser) = @_;

      ($self->{type}, $self->{id}, $self->{variant})
   }

   sub My::Object::THAW {
      my ($class, $serialiser, $type, $id, $variant) = @_;

      $class-<new (type => $type, id => $id, variant => $variant)
   }

=head1 BUGS

The use of L<overload> makes this module much heavier than it should be
(on my system, this module: 4kB RSS, overload: 260kB RSS).

=head1 SEE ALSO

Currently, L<JSON::XS> and L<CBOR::XS> use these types.

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

1

Revision:	1.3
Committed:	Sun Oct 27 22:46:21 2013 UTC (10 years, 8 months ago) by root
Branch:	MAIN
Changes since 1.2:	+54 -0 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			Types::Serialiser - simple data types for common serialisation formats
4
5			=encoding utf-8
6
7			=head1 SYNOPSIS
8
9			=head1 DESCRIPTION
10
11			This module provides some extra datatypes that are used by common
12			serialisation formats such as JSON or CBOR. The idea is to have a
13			repository of simple/small constants and containers that can be shared by
14			different implementations so they become interoperable between each other.
15
16			=cut
17
18			package Types::Serialiser;
19
20			our $VERSION = 0.01;
21
22			=head1 SIMPLE SCALAR CONSTANTS
23
24			Simple scalar constants are values that are overloaded to act like simple
25			Perl values, but have (class) type to differentiate them from normal Perl
26			scalars. This is necessary because these have different representations in
27			the serialisation formats.
28
29			=head2 BOOLEANS (Types::Serialiser::Boolean class)
30
31			This type has only two instances, true and false. A natural representation
32			for these in Perl is C<1> and C<0>, but serialisation formats need to be
33			able to differentiate between them and mere numbers.
34
35			=over 4
36
37			=item $Types::Serialiser::true, Types::Serialiser::true
38
39			This value represents the "true" value. In most contexts is acts like
40			the number C<1>. It is up to you whether you use the variable form
41			(C<$Types::Serialiser::true>) or the constant form (C<Types::Serialiser::true>).
42
43			The constant is represented as a reference to a scalar containing C<1> -
44			implementations are allowed to directly test for this.
45
46			=item $Types::Serialiser::false, Types::Serialiser::false
47
48			This value represents the "false" value. In most contexts is acts like
49			the number C<0>. It is up to you whether you use the variable form
50			(C<$Types::Serialiser::false>) or the constant form (C<Types::Serialiser::false>).
51
52			The constant is represented as a reference to a scalar containing C<0> -
53			implementations are allowed to directly test for this.
54
55			=item $is_bool = Types::Serialiser::is_bool $value
56
57			Returns true iff the C<$value> is either C<$Types::Serialiser::true> or
58			C<$Types::Serialiser::false>.
59
60			For example, you could differentiate between a perl true value and a
61			C<Types::Serialiser::true> by using this:
62
63			$value && Types::Serialiser::is_bool $value
64
65			=item $is_true = Types::Serialiser::is_true $value
66
67			Returns true iff C<$value> is C<$Types::Serialiser::true>.
68
69			=item $is_false = Types::Serialiser::is_false $value
70
71			Returns false iff C<$value> is C<$Types::Serialiser::false>.
72
73			=back
74
75			=head2 ERROR (Types::Serialiser::Error class)
76
77			This class has only a single instance, C<error>. It is used to signal
78			an encoding or decoding error. In CBOR for example, and object that
79			couldn't be encoded will be represented by a CBOR undefined value, which
80			is represented by the error value in Perl.
81
82			=over 4
83
84			=item $Types::Serialiser::error, Types::Serialiser::error
85
86			This value represents the "error" value. Accessing values of this type
87			will throw an exception.
88
89			The constant is represented as a reference to a scalar containing C<undef>
90			- implementations are allowed to directly test for this.
91
92			=item $is_error = Types::Serialiser::is_error $value
93
94			Returns false iff C<$value> is C<$Types::Serialiser::error>.
95
96			=back
97
98			=cut
99
100			our $true = do { bless \(my $dummy = 1), Types::Serialiser::Boolean:: };
101			our $false = do { bless \(my $dummy = 0), Types::Serialiser::Boolean:: };
102			our $error = do { bless \(my $dummy ), Types::Serialiser::Error:: };
103
104			sub true () { $true }
105			sub false () { $false }
106			sub error () { $error }
107
108			sub is_bool ($) { UNIVERSAL::isa $_[0], Types::Serialiser::Boolean:: }
109			sub is_true ($) { $_[0] && UNIVERSAL::isa $_[0], Types::Serialiser::Boolean:: }
110			sub is_false ($) { !$_[0] && UNIVERSAL::isa $_[0], Types::Serialiser::Boolean:: }
111			sub is_error ($) { UNIVERSAL::isa $_[0], Types::Serialiser::Error:: }
112
113			package Types::Serialiser::Boolean;
114
115			use overload
116			"0+" => sub { ${$_[0]} },
117			"++" => sub { $_[0] = ${$_[0]} + 1 },
118			"--" => sub { $_[0] = ${$_[0]} - 1 },
119			fallback => 1;
120
121			package Types::Serialiser::Error;
122
123			sub error {
124			require Carp;
125	root	1.2	Carp::croak ("caught attempt to use the Types::Serialiser::error value");
126	root	1.1	};
127
128			use overload
129			"0+" => \&error,
130			"++" => \&error,
131			"--" => \&error,
132			fallback => 1;
133
134	root	1.2	=head1 NOTES FOR XS USERS
135
136			The recommended way to detect whether a scalar is one of these objects
137			is to check whether the stash is the C<Types::Serialiser::Boolean> or
138			C<Types::Serialiser::Error> stash, and then follow the scalar reference to
139			see if it's C<1> (true), C<0> (false) or C<undef> (error).
140
141			While it is possible to use an isa test, directly comparing stash pointers
142			is faster and guaranteed to work.
143
144	root	1.3	=head1 A GENERIC OBJECT SERIALIATION PROTOCOL
145
146			This section explains the object serialisation protocol used by
147			L<CBOR::XS>. It is meant to be generic enough to support any kind of
148			generic object serialiser.
149
150			This protocol is called "the Types::Serialiser object serialisation
151			protocol".
152
153			=head2 ENCODING
154
155			When the encoder encounters an object that it cannot otherwise encode (for
156			example, L<CBOR::XS> can encode a few special types itself, and will first
157			attempt to use the special C<TO_CBOR> serialisation protocol), it will
158			look up the C<FREEZE> method on the object.
159
160			If it exists, it will call it with two arguments: the object to
161			serialise, and a constant string that indicates the name of the
162			serialisationformat. For example L<CBOR::XS> uses C<CBOR>, and L<JSON> and
163			L<JSON::XS> (or any other JSON serialiser), would use C<JSON> as second
164			argument.
165
166			The C<FREEZE> method can then return zero or more values to identify the
167			object instance. The serialiser is then supposed to encode the class name
168			and all of these return values (which must be encodable in the format)
169			using the relevant form for perl objects. In CBOR for example, there is a
170			registered tag number for encoded perl objects.
171
172			=head2 DECODING
173
174			When the decoder then encounters such an encoded perl object, it should
175			look up the C<THAW> method on the stored classname, and invoke it with the
176			classname, the constant string to identify the format, and all the return
177			values returned by C<FREEZE>.
178
179			=head2 EXAMPLES
180
181			See the C<OBJECT SERIALISATION> section in the L<CBOR::XS> manpage for
182			more details, an example implementation, and code examples.
183
184			Here is an example C<FREEZE>/C<THAW> method pair:
185
186			sub My::Object::FREEZE {
187			my ($self, $serialiser) = @_;
188
189			($self->{type}, $self->{id}, $self->{variant})
190			}
191
192			sub My::Object::THAW {
193			my ($class, $serialiser, $type, $id, $variant) = @_;
194
195			$class-<new (type => $type, id => $id, variant => $variant)
196			}
197
198	root	1.1	=head1 BUGS
199
200			The use of L<overload> makes this module much heavier than it should be
201			(on my system, this module: 4kB RSS, overload: 260kB RSS).
202
203			=head1 SEE ALSO
204
205			Currently, L<JSON::XS> and L<CBOR::XS> use these types.
206
207			=head1 AUTHOR
208
209			Marc Lehmann <schmorp@schmorp.de>
210			http://home.schmorp.de/
211
212			=cut
213
214			1
215