jsonv::polymorphic_adapter< TPointer > Class Template Reference

An adapter which can create polymorphic types. More...

#include <jsonv/serialization/polymorphic_adapter.hpp>

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Public Types
using	match_predicate = std::function< bool(deserialization_context &, const value &)>

Public Member Functions
template<typename T >
void	add_subtype (match_predicate pred)
	Add a subtype which can be transformed into TPointer which will be called if the discriminator pred is matched.
template<typename T >
void	add_subtype_keyed (std::string key, value expected_value, keyed_subtype_action action=keyed_subtype_action::none)
	Add a subtype which can be transformed into TPointer which will be called if given a JSON value with kind::object which has a member with key and the provided expected_value.
void	check_null_input (bool on)
	When deserializing a C++ value, should kind::null in JSON automatically become a default-constructed TPointer (which is usually the null representation)?
bool	check_null_input () const
	When deserializing a C++ value, should kind::null in JSON automatically become a default-constructed TPointer (which is usually the null representation)?
void	check_null_output (bool on)
	When serializing, should an empty TPointer be written as null?
bool	check_null_output () const
	When serializing, should an empty TPointer be written as null?
Public Member Functions inherited from jsonv::adapter_for< TPointer >
virtual const std::type_info &	get_type () const noexcept override
virtual std::expected< void, ast_node_type >	deserialize (deserialization_context &context, reader &from, void *into) const override
virtual void	serialize (const serialization_context &context, const void *from, writer &to) const override

Protected Member Functions
virtual std::expected< TPointer, ast_node_type >	create (deserialization_context &context, reader &from) const override
	Create an instance of T by reading from.
virtual void	serialize (const serialization_context &context, const TPointer &from, writer &to) const override
	Write the object from points to where to is, or null for an empty pointer under check_null_output.

Detailed Description

template<typename TPointer>
class jsonv::polymorphic_adapter< TPointer >

An adapter which can create polymorphic types.

This allows you to parse JSON directly into a type heirarchy without some middle layer.

[
  {
    "type": "worker",
    "name": "Adam"
  },
  {
    "type": "manager",
    "name": "Bob",
    "head": "Development"
  }
]

Choosing a subtype means looking at the value before deserializing it, which a reader – a forward cursor – cannot do by itself. Each discriminator is shown as little of the value as answers it, read without moving the reader, and the subtype it picks is then deserialized from the reader directly:

• From a value, every discriminator is shown that value. Nothing is copied.
• From JSON text, one registered with add_subtype_keyed is shown an object holding only the discriminating members, found by stepping over every other member whole. One registered with add_subtype can ask anything of the value, so the first time one of those has to be asked the subtree is materialised for it. Registering the keyed subtypes first keeps a matching document from ever being materialised.

Serializing writes the pointed-to object where the writer is, through the serializer registered for its dynamic type. A subtype registered with keyed_subtype_action::check or keyed_subtype_action::insert is the exception, since the action works on the finished object: it is built as a value through serialization_context::to_json, checked or completed, and only then written whole. Its members therefore come out sorted by key, as they do from to_json, and a serialization_error raised inside it reports a path from its own root rather than the document's. One the action refuses has written nothing.

Template Parameters

TPointer

Some pointer-like type (likely unique_ptr or shared_ptr) you wish to deserialize values into. It must support operator*, an explicit conversion to bool, construction with a pointer to a subtype of what it contains and default construction.

Definition at line 88 of file polymorphic_adapter.hpp.

Member Typedef Documentation

match_predicate

template<typename TPointer >

using jsonv::polymorphic_adapter< TPointer >::match_predicate = std::function<bool (deserialization_context&, const value&)>

Definition at line 92 of file polymorphic_adapter.hpp.

Member Function Documentation

add_subtype()

template<typename TPointer >

template<typename T >

void jsonv::polymorphic_adapter< TPointer >::add_subtype ( match_predicate  pred )

inline

Add a subtype which can be transformed into TPointer which will be called if the discriminator pred is matched.

See also

add_subtype_keyed

Definition at line 102 of file polymorphic_adapter.hpp.

add_subtype_keyed()

template<typename TPointer >

template<typename T >

void jsonv::polymorphic_adapter< TPointer >::add_subtype_keyed ( std::string  key, value  expected_value, keyed_subtype_action  action = keyed_subtype_action::none  )

inline

Add a subtype which can be transformed into TPointer which will be called if given a JSON value with kind::object which has a member with key and the provided expected_value.

See also

add_subtype

Definition at line 112 of file polymorphic_adapter.hpp.

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check_null_input() [1/2]

template<typename TPointer >

bool jsonv::polymorphic_adapter< TPointer >::check_null_input ( ) const

inline

When deserializing a C++ value, should kind::null in JSON automatically become a default-constructed TPointer (which is usually the null representation)?

Definition at line 145 of file polymorphic_adapter.hpp.

check_null_input() [2/2]

template<typename TPointer >

void jsonv::polymorphic_adapter< TPointer >::check_null_input ( bool  on )

inline

When deserializing a C++ value, should kind::null in JSON automatically become a default-constructed TPointer (which is usually the null representation)?

Definition at line 139 of file polymorphic_adapter.hpp.

check_null_output() [1/2]

template<typename TPointer >

bool jsonv::polymorphic_adapter< TPointer >::check_null_output ( ) const

inline

When serializing, should an empty TPointer be written as null?

Definition at line 160 of file polymorphic_adapter.hpp.

check_null_output() [2/2]

template<typename TPointer >

void jsonv::polymorphic_adapter< TPointer >::check_null_output ( bool  on )

inline

When serializing, should an empty TPointer be written as null?

Definition at line 154 of file polymorphic_adapter.hpp.

create()

template<typename TPointer >

virtual std::expected< TPointer, ast_node_type > jsonv::polymorphic_adapter< TPointer >::create ( deserialization_context &  context, reader &  from  ) const

inlineoverrideprotectedvirtual

Create an instance of T by reading from.

Parameters

context	Extra information to help you decode sub-objects, such as looking up other deserializer implementations via formats. Record any problem you encounter with deserialization_context::problem.
from	The JSON reader to deserialize from. On a successful return it should sit one position past the value which was read, as reader::next_value would have left it.

Returns

The created instance; otherwise a std::unexpected carrying the ast_node_type actually found when the failure was a type mismatch, or ast_node_type::error otherwise.

Implements jsonv::adapter_for< TPointer >.

Definition at line 168 of file polymorphic_adapter.hpp.

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serialize()

template<typename TPointer >

virtual void jsonv::polymorphic_adapter< TPointer >::serialize ( const serialization_context &  context, const TPointer &  from, writer &  to  ) const

inlineoverrideprotectedvirtual

Write the object from points to where to is, or null for an empty pointer under check_null_output.

A subtype registered with keyed_subtype_action::check or keyed_subtype_action::insert is built as a value and written whole, as the class description says.

Implements jsonv::adapter_for< TPointer >.

Definition at line 258 of file polymorphic_adapter.hpp.

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The documentation for this class was generated from the following file:

• jsonv/serialization/polymorphic_adapter.hpp