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
($Types::Serialiser::true) or the constant form (Types::Serialiser::true).
The constant is represented as a reference to a scalar containing 1 - implementations are allowed to directly test for this.
This value represents the false value. In most contexts is acts like
the number 0. It is up to you whether you use the variable form
($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 $Types::Serialiser::true or
|$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.|
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 couldnt 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.
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 its 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).
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.
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.
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.
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:
The use of overload makes this module much heavier than it should be (on my system, this module: 4kB RSS, overload: 260kB RSS).
Marc Lehmann <firstname.lastname@example.org> http://home.schmorp.de/
|perl v5.20.3||SERIALISER (3)||2013-11-30|