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nlohmann
125 lines
3.0 KiB
Markdown
125 lines
3.0 KiB
Markdown
# Architecture
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!!! info
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This page is still under construction. Its goal is to provide a high-level overview of the library's architecture.
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This should help new contributors to get an idea of the used concepts and where to make changes.
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## Overview
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The main structure is class [nlohmann::basic_json](../api/basic_json/index.md).
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- public API
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- container interface
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- iterators
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## Template specializations
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- describe template parameters of `basic_json`
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- [`json`](../api/json.md)
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- [`ordered_json`](../api/ordered_json.md) via [`ordered_map`](../api/ordered_map.md)
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## Value storage
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Values are stored as a tagged union of [value_t](../api/basic_json/value_t.md) and json_value.
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```cpp
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/// the type of the current element
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value_t m_type = value_t::null;
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/// the value of the current element
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json_value m_value = {};
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```
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with
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```cpp
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enum class value_t : std::uint8_t
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{
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null, ///< null value
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object, ///< object (unordered set of name/value pairs)
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array, ///< array (ordered collection of values)
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string, ///< string value
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boolean, ///< boolean value
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number_integer, ///< number value (signed integer)
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number_unsigned, ///< number value (unsigned integer)
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number_float, ///< number value (floating-point)
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binary, ///< binary array (ordered collection of bytes)
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discarded ///< discarded by the parser callback function
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};
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union json_value {
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/// object (stored with pointer to save storage)
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object_t *object;
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/// array (stored with pointer to save storage)
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array_t *array;
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/// string (stored with pointer to save storage)
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string_t *string;
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/// binary (stored with pointer to save storage)
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binary_t *binary;
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/// boolean
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boolean_t boolean;
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/// number (integer)
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number_integer_t number_integer;
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/// number (unsigned integer)
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number_unsigned_t number_unsigned;
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/// number (floating-point)
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number_float_t number_float;
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};
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```
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## Parsing inputs (deserialization)
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Input is read via **input adapters** that abstract a source with a common interface:
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```cpp
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/// read a single character
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std::char_traits<char>::int_type get_character() noexcept;
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/// read multiple characters to a destination buffer and
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/// returns the number of characters successfully read
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template<class T>
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std::size_t get_elements(T* dest, std::size_t count = 1);
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```
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List examples of input adapters.
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## SAX Interface
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TODO
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## Writing outputs (serialization)
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Output is written via **output adapters**:
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```cpp
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template<typename T>
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void write_character(CharType c);
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template<typename CharType>
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void write_characters(const CharType* s, std::size_t length);
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```
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List examples of output adapters.
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## Value conversion
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```cpp
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template<class T>
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void to_json(basic_json& j, const T& t);
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template<class T>
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void from_json(const basic_json& j, T& t);
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```
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## Additional features
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- JSON Pointers
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- Binary formats
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- Custom base class
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- Conversion macros
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## Details namespace
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- C++ feature backports
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