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Serialiser(3)         User Contributed Perl Documentation        Serialiser(3)
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 with
       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.
       Note that the "FREEZE" method will normally be called during encoding,
       and MUST NOT change the data structure that is being encoded in any
       way, or it might cause memory corruption or worse.
       If it exists, it will call it with two arguments: the object to
       serialise, and a constant string that indicates the name of the data
       model. For example CBOR::XS uses "CBOR", and the JSON and JSON::XS
       modules (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.
       The values that "FREEZE" returns must be serialisable with the
       serialiser that calls it. Therefore, it is recommended to use simple
       types such as strings and numbers, and maybe array references and
       hashes (basically, the JSON data model). You can always use a more
       complex format for a specific data model by checking the second
       argument, the data model.
       The "data model" is not the same as the "data format" - the data model
       indicates what types and kinds of return values can be returned from
       "FREEZE". For example, in "CBOR" it is permissible to return tagged
       CBOR values, while JSON does not support these at all, so "JSON" would
       be a valid (but too limited) data model name for "CBOR::XS". similarly,
       a serialising format that supports more or less the same data model as
       JSON could use "JSON" as data model without losing anything.
   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 data model/data
       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, $model) = @_;
             ($self->{type}, $self->{id}, $self->{variant})
          }
          sub My::Object::THAW {
             my ($class, $model, $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 AT schmorp.de>
        http://home.schmorp.de/
perl v5.26.3                      2019-10-14                     Serialiser(3)