Niels Lohmann
a47170346a
* docs: new design for the documentation site Apply the brand to the Material for MkDocs site: Inter and JetBrains Mono served by the site (upright and real italic), brand colours, blue header band with the syntax pattern, wordmark in the header, new home page (hero, cards, animated feature tour), 404 page, polish for tabs, search, footer, focus rings, tables and code blocks, and theme features (code copy, previous/next footer, TOC follow, search suggestions). Draw the number railroad diagram, the parser callback events and the iterator illustrations as inline SVGs that follow the light and dark scheme. The generator scripts are in docs/mkdocs/scripts/figures; the feature slideshow (json-light.svg, json-dark.svg, replacing json.gif on the home page) is built by docs/mkdocs/scripts/slideshow. Decision nodes in five flowcharts become hexagons, which need far less room. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: add figures, table captions and a macro chooser - Figures with numbered captions: SAX stepper, json_view layout and edit stepper, exception map, JSON pointer and patch walkers, QA pipeline, scaling and binary size charts, roadmap lanes, release timeline, integration decision tree and namespace builder - Table captions (nj-table-caption) on 9 pages - Compile times: modules and PCH charts, filesystem section, re-measured Figure 1, links between features/modules.md and compile_times.md - Interactive macro chooser for features/arbitrary_types.md - Link check: exclude URLs that answer the plugin with 400/401/419 or are dead (customers.md) Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: macro chooser generates adl_serializer for non-default-constructible types Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: cross-link concept pages and API pages in See also sections Add See also links in both directions between the concept pages (features, home, integration) and the API pages, write API links in code font, give every entry a comment after a dash, and show the callback event figure on the parser callbacks page. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * docs: address review comments on the new design - Home: add a "Latest release" button - Sponsors: update the list and group it by tier - Features: list all feature pages on the index page - Releases: add highlights per release, link the 4.0 roadmap, add the first commit to the timeline - Exceptions: prefix all example messages with the exception name - API: no code font for format names in the See also links of the to_/from_ pages - Merge Patch: show the document before, the patch, and the result - Replace "--" with typographic dashes, mark external links with an icon, center Mermaid diagrams Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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3.6 KiB
NLOHMANN_JSON_SERIALIZE_ENUM
#define NLOHMANN_JSON_SERIALIZE_ENUM(type, conversion...)
By default, enum values are serialized to JSON as integers. In some cases, this could result in undesired behavior. If an enum is modified or re-ordered after data has been serialized to JSON, the later deserialized JSON data may be undefined or a different enum value than was originally intended.
The NLOHMANN_JSON_SERIALIZE_ENUM allows to define a user-defined serialization for every enumerator.
Parameters
type(in)- name of the enum to serialize/deserialize
conversion(in)- a pair of an enumerator and a JSON serialization; arbitrary pairs can be given as a comma-separated list
Default definition
The macro adds two functions to the namespace which take care of the serialization and deserialization:
template<typename BasicJsonType>
inline void to_json(BasicJsonType& j, const type& e);
template<typename BasicJsonType>
inline void from_json(const BasicJsonType& j, type& e);
Notes
!!! info "Prerequisites"
The macro must be used inside the namespace of the enum.
!!! important "Important notes"
- When using [`get<ENUM_TYPE>()`](../basic_json/get.md), undefined JSON values will default to the first specified
conversion. Select this default pair carefully. See example 1 below.
- If an enum or JSON value is specified in multiple conversions, the first matching conversion from the top of the
list will be returned when converting to or from JSON. See example 2 below.
- Maps with enum keys (e.g., `std::map<ENUM_TYPE, T>`) are stored as arrays of `[key, value]` pairs by default.
Define [`JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS`](json_use_objects_for_enum_keyed_maps.md) to store them as objects
with the converted keys. Such maps can be read from both forms.
!!! info "Views"
The generated `from_json()` also reads the views of [`json_document`](../json_document.md)s
(`<nlohmann/json_view.hpp>`), comparing the view with the entries of the mapping, without building a `json` value
first.
Examples
??? example "Example: Basic usage"
The example shows how `NLOHMANN_JSON_SERIALIZE_ENUM` can be used to serialize/deserialize both classical enums and
C++11 enum classes:
```cpp hl_lines="16 17 18 19 20 21 22 29 30 31 32 33"
--8<-- "examples/nlohmann_json_serialize_enum.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum.output"
```
??? example "Example: Multiple conversions for one enumerator"
The example shows how to use multiple conversions for a single enumerator. In the example, `Color::red` will always
be *serialized* to `"red"`, because the first occurring conversion. The second conversion, however, offers an
alternative *deserialization* from `"rot"` to `Color::red`.
```cpp hl_lines="17"
--8<-- "examples/nlohmann_json_serialize_enum_2.cpp"
```
Output:
```json
--8<-- "examples/nlohmann_json_serialize_enum_2.output"
```
See also
- Specializing enum conversion - serializing enums as JSON strings
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT- strict variant that throws on unmapped valuesJSON_DISABLE_ENUM_SERIALIZATION- disable the default enum conversionJSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS- serialize maps with enum keys as objects
Version history
Added in version 3.4.0.
The generated from_json() reads the views of json_documents since version 3.13.0.