[ViewVC] Annotation of: cvs/Types-Serialiser/README

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

SYNOPSIS
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.

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.

  BOOLEANS (Types::Serialiser::Boolean class)
    This type has only two instances, true and false. A natural
    representation for these in Perl is 1 and 0, but serialisation formats
    need to be able to differentiate between them and mere numbers.

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

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

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

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

    $is_bool = Types::Serialiser::is_bool $value
        Returns true iff the $value is either $Types::Serialiser::true or
        $Types::Serialiser::false.

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

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

    $is_true = Types::Serialiser::is_true $value
        Returns true iff $value is $Types::Serialiser::true.

    $is_false = Types::Serialiser::is_false $value
        Returns false iff $value is $Types::Serialiser::false.

  ERROR (Types::Serialiser::Error class)
    This class has only a single instance, "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.

    $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
        "undef" - implementations are allowed to directly test for this.

    $is_error = Types::Serialiser::is_error $value
        Returns false iff $value is $Types::Serialiser::error.

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 "Types::Serialiser::Boolean" or
    "Types::Serialiser::Error" stash, and then follow the scalar reference
    to see if it's 1 (true), 0 (false) or "undef" (error).

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

    For historical reasons, the "Types::Serialiser::Boolean" stash is just
    an alias for "JSON::PP::Boolean". When printed, the classname withh
    usually be "JSON::PP::Boolean", but isa tests and stash pointer
    comparison will normally work correctly (i.e. Types::Serialiser::true
    ISA JSON::PP::Boolean, but also ISA Types::Serialiser::Boolean).

A GENERIC OBJECT SERIALIATION PROTOCOL
    This section explains the object serialisation protocol used by
    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".

  ENCODING
    When the encoder encounters an object that it cannot otherwise encode
    (for example, CBOR::XS can encode a few special types itself, and will
    first attempt to use the special "TO_CBOR" serialisation protocol), it
    will look up the "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 CBOR::XS uses "CBOR", and JSON and
    JSON::XS (or any other JSON serialiser), would use "JSON" as second
    argument.

    The "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.

  DECODING
    When the decoder then encounters such an encoded perl object, it should
    look up the "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 "FREEZE".

  EXAMPLES
    See the "OBJECT SERIALISATION" section in the CBOR::XS manpage for more
    details, an example implementation, and code examples.

    Here is an example "FREEZE"/"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)
       }

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

SEE ALSO
    Currently, JSON::XS and CBOR::XS use these types.

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

Revision:	1.3
Committed:	Mon Oct 28 15:29:28 2013 UTC (10 years, 8 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_02
Changes since 1.2:	+56 -0 lines
Log Message:	0.02
#	User	Rev	Content
1	root	1.2	NAME
2			Types::Serialiser - simple data types for common serialisation formats
3
4			SYNOPSIS
5			DESCRIPTION
6			This module provides some extra datatypes that are used by common
7			serialisation formats such as JSON or CBOR. The idea is to have a
8			repository of simple/small constants and containers that can be shared
9			by different implementations so they become interoperable between each
10			other.
11
12			SIMPLE SCALAR CONSTANTS
13			Simple scalar constants are values that are overloaded to act like
14			simple Perl values, but have (class) type to differentiate them from
15			normal Perl scalars. This is necessary because these have different
16			representations in the serialisation formats.
17
18			BOOLEANS (Types::Serialiser::Boolean class)
19			This type has only two instances, true and false. A natural
20			representation for these in Perl is 1 and 0, but serialisation formats
21			need to be able to differentiate between them and mere numbers.
22
23			$Types::Serialiser::true, Types::Serialiser::true
24			This value represents the "true" value. In most contexts is acts
25			like the number 1. It is up to you whether you use the variable form
26			($Types::Serialiser::true) or the constant form
27			("Types::Serialiser::true").
28
29			The constant is represented as a reference to a scalar containing 1
30			- implementations are allowed to directly test for this.
31
32			$Types::Serialiser::false, Types::Serialiser::false
33			This value represents the "false" value. In most contexts is acts
34			like the number 0. It is up to you whether you use the variable form
35			($Types::Serialiser::false) or the constant form
36			("Types::Serialiser::false").
37
38			The constant is represented as a reference to a scalar containing 0
39			- implementations are allowed to directly test for this.
40
41			$is_bool = Types::Serialiser::is_bool $value
42			Returns true iff the $value is either $Types::Serialiser::true or
43			$Types::Serialiser::false.
44
45			For example, you could differentiate between a perl true value and a
46			"Types::Serialiser::true" by using this:
47
48			$value && Types::Serialiser::is_bool $value
49
50			$is_true = Types::Serialiser::is_true $value
51			Returns true iff $value is $Types::Serialiser::true.
52
53			$is_false = Types::Serialiser::is_false $value
54			Returns false iff $value is $Types::Serialiser::false.
55
56			ERROR (Types::Serialiser::Error class)
57			This class has only a single instance, "error". It is used to signal an
58			encoding or decoding error. In CBOR for example, and object that
59			couldn't be encoded will be represented by a CBOR undefined value, which
60			is represented by the error value in Perl.
61
62			$Types::Serialiser::error, Types::Serialiser::error
63			This value represents the "error" value. Accessing values of this
64			type will throw an exception.
65
66			The constant is represented as a reference to a scalar containing
67			"undef" - implementations are allowed to directly test for this.
68
69			$is_error = Types::Serialiser::is_error $value
70			Returns false iff $value is $Types::Serialiser::error.
71
72			NOTES FOR XS USERS
73			The recommended way to detect whether a scalar is one of these objects
74			is to check whether the stash is the "Types::Serialiser::Boolean" or
75			"Types::Serialiser::Error" stash, and then follow the scalar reference
76			to see if it's 1 (true), 0 (false) or "undef" (error).
77
78			While it is possible to use an isa test, directly comparing stash
79			pointers is faster and guaranteed to work.
80
81	root	1.3	For historical reasons, the "Types::Serialiser::Boolean" stash is just
82			an alias for "JSON::PP::Boolean". When printed, the classname withh
83			usually be "JSON::PP::Boolean", but isa tests and stash pointer
84			comparison will normally work correctly (i.e. Types::Serialiser::true
85			ISA JSON::PP::Boolean, but also ISA Types::Serialiser::Boolean).
86
87			A GENERIC OBJECT SERIALIATION PROTOCOL
88			This section explains the object serialisation protocol used by
89			CBOR::XS. It is meant to be generic enough to support any kind of
90			generic object serialiser.
91
92			This protocol is called "the Types::Serialiser object serialisation
93			protocol".
94
95			ENCODING
96			When the encoder encounters an object that it cannot otherwise encode
97			(for example, CBOR::XS can encode a few special types itself, and will
98			first attempt to use the special "TO_CBOR" serialisation protocol), it
99			will look up the "FREEZE" method on the object.
100
101			If it exists, it will call it with two arguments: the object to
102			serialise, and a constant string that indicates the name of the
103			serialisationformat. For example CBOR::XS uses "CBOR", and JSON and
104			JSON::XS (or any other JSON serialiser), would use "JSON" as second
105			argument.
106
107			The "FREEZE" method can then return zero or more values to identify the
108			object instance. The serialiser is then supposed to encode the class
109			name and all of these return values (which must be encodable in the
110			format) using the relevant form for perl objects. In CBOR for example,
111			there is a registered tag number for encoded perl objects.
112
113			DECODING
114			When the decoder then encounters such an encoded perl object, it should
115			look up the "THAW" method on the stored classname, and invoke it with
116			the classname, the constant string to identify the format, and all the
117			return values returned by "FREEZE".
118
119			EXAMPLES
120			See the "OBJECT SERIALISATION" section in the CBOR::XS manpage for more
121			details, an example implementation, and code examples.
122
123			Here is an example "FREEZE"/"THAW" method pair:
124
125			sub My::Object::FREEZE {
126			my ($self, $serialiser) = @_;
127
128			($self->{type}, $self->{id}, $self->{variant})
129			}
130
131			sub My::Object::THAW {
132			my ($class, $serialiser, $type, $id, $variant) = @_;
133
134			$class-<new (type => $type, id => $id, variant => $variant)
135			}
136
137	root	1.2	BUGS
138			The use of overload makes this module much heavier than it should be (on
139			my system, this module: 4kB RSS, overload: 260kB RSS).
140
141			SEE ALSO
142			Currently, JSON::XS and CBOR::XS use these types.
143
144			AUTHOR
145			Marc Lehmann <schmorp@schmorp.de>
146			http://home.schmorp.de/
147