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Niels Lohmann
63c10a51fc
* Review and extend the documentation, and check it in CI A review of all documentation pages found factual errors, dead links, missing cross-references, and gaps in examples. This fixes them and adds checks so the same problems are caught automatically. Fixes: - wrong signatures and version histories (operator!= C++20 member, binary() subtype type, get<PointerType>(), JSON_NO_THREAD_LOCAL, ...) - stale descriptions (number parsing since #5283, UBJSON table, SAX example that no longer compiled, tsl::ordered_map advice) - dead internal and external links; repology.org badges (the domain is suspended) replaced by badges that query the registries directly - deprecation notes link the migration guide; the guide itself fixed Additions: - "See also" sections, cross-references, 25 runnable examples, 12 Mermaid diagrams, new API pages for json_pointer::operator<=> and byte_container_with_subtype::operator==/!= - landing page, guides for untrusted input and performance - "unreleased" badge after versions newer than the latest release Checks: - strict documentation build (broken links/anchors fail it); CI and the publish workflow fetch the full history the build needs - weekly external link check, Mermaid syntax check in CI - check_structure.py: example titles, heading levels, alt texts, header links, docset index coverage; its unused-example check works again - all examples produce the same output on every platform Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Keep the customer links that could not be fixed A dead link on the customers page is still the evidence of where the use of the library was documented. Keep the original URLs of the entries without a working replacement (Marne, Cisco Webex Desk Camera, Philips Hue, CyberArk) and exclude exactly these URLs from the link check. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Correct the duplicate-key recipe's claim about SAX positions The SAX interface's key() receives no position either; only parse_error() does. Also note that the recipe does not report the path to the repeated key (see discussion #5085). Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Say the library is available as a single header and mention json_fwd.hpp Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Correct documentation errors found while hunting for bugs - patch/patch_inplace: list the JSON pointer errors parse_error.106-109 and out_of_range.402/404, and quote the actual parse_error.105 message. - unflatten: list parse_error.106/107/108 and out_of_range.404. - to_bson: list out_of_range.415 (binary subtype above 255) and note that 412 and 415 are new in 3.13.0. - to_string: state that string_t must be convertible to std::string, also in the StringType requirements table. - JSON Lines: a `while (input >> j)` loop also throws after the last value for concatenated JSON values; show a loop that works for both. - BON8: a string gets 0xFF only if nothing follows it in the message; a string at the end of an array or object is ended by 0xFE. - custom_string_type.hpp: add operator+=(char), which the "Always required" list asks for (json_pointer::to_string, flatten, unflatten, and diff did not compile), and an ADL int_to_string for diff and items. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Cache the release headers with functools.lru_cache Codacy (Pylint) flagged the mutable default argument that header() used as its cache. functools.lru_cache keeps the same memoization without it. The script's output is unchanged. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>
83 lines
3.3 KiB
Markdown
83 lines
3.3 KiB
Markdown
# <small>nlohmann::basic_json::</small>unflatten
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```cpp
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basic_json unflatten() const;
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```
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The function restores the arbitrary nesting of a JSON value that has been flattened before using the
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[`flatten()`](flatten.md) function. The JSON value must meet certain constraints:
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1. The value must be an object.
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2. The keys must be JSON pointers (see [RFC 6901](https://tools.ietf.org/html/rfc6901))
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3. The mapped values must be primitive JSON types.
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## Return value
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the original JSON from a flattened version
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## Exception safety
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Strong exception safety: if an exception occurs, the original value stays intact.
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## Exceptions
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The function can throw the following exceptions:
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- Throws [`type_error.314`](../../home/exceptions.md#jsonexceptiontype_error314) if value is not an object
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- Throws [`type_error.315`](../../home/exceptions.md#jsonexceptiontype_error315) if object values are not primitive
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- Throws [`type_error.313`](../../home/exceptions.md#jsonexceptiontype_error313) if a key (JSON pointer) leads to a
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conflicting nesting; example: `"invalid value to unflatten"`
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- Throws [`parse_error.106`](../../home/exceptions.md#jsonexceptionparse_error106) if an array index in a key begins
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with '0'; example: `"array index '01' must not begin with '0'"`
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- Throws [`parse_error.107`](../../home/exceptions.md#jsonexceptionparse_error107) if a key is not empty and does not
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begin with a slash (`/`); example: `"JSON pointer must be empty or begin with '/' - was: 'a'"`
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- Throws [`parse_error.108`](../../home/exceptions.md#jsonexceptionparse_error108) if a tilde (`~`) in a key is not
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followed by `0` or `1`; example: `"escape character '~' must be followed with '0' or '1'"`
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- Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) if an array index in a key is not a
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number; example: `"array index 'one' is not a number"`
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- Throws [`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) if a level becomes an array
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(because one of its keys is `0`) and another key at that level cannot be an array index; example:
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`"unresolved reference token 'x'"`
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## Complexity
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Linear in the size of the JSON value.
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## Notes
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Empty objects and arrays are flattened by [`flatten()`](flatten.md) to `#!json null` values and cannot unflattened to
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their original type.
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A flattened array and a flattened object whose keys are array indices are indistinguishable, because both are
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described by the same JSON pointers. A value is therefore restored as an array if and only if one of its keys is the
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reference token `0`, and as an object otherwise: `#!json {"2": 1}` is restored unchanged, whereas `#!json {"0": 1}` is
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restored as `#!json [1]`. This decision does not depend on the order in which the flattened object is iterated.
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Apart from these two cases, for a JSON value `j`, the following is always true:
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`#!cpp j == j.flatten().unflatten()`.
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## Examples
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??? example
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The following code shows how a flattened JSON object is unflattened into the original nested JSON object.
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```cpp
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--8<-- "examples/unflatten.cpp"
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```
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Output:
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```json
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--8<-- "examples/unflatten.output"
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```
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## See also
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- [flatten](flatten.md) the reverse function
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## Version history
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- Added in version 2.0.0.
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- Made the array/object decision independent of the object's iteration order in version 3.13.0.
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