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Niels Lohmann
4303ba674d
Add json_document and json_view, a read-only, zero-copy index of a JSON text, as the first public slice of the zero-copy view (#5295). A parse produces a flat array of 16-byte nodes in document order, one per value and one per object key. Strings stay in the source text; escaped strings are decoded into an arena. Integers are converted while their digits are in the cache; floats keep only their digit layout and are converted on read. Containers store the size of their subtree, so a reader can step over one in constant time. A document makes a handful of allocations, however many values it has. The parser accepts exactly what json::parse accepts, with every combination of ignore_comments and ignore_trailing_commas, with and without a trailing NUL, and under JSON_STRICT_NUL_HANDLING. It is portable C++11 and does not depend on byte order. basic_json_document adds parse, parse_copy, accept, read (reuses a document's memory), root, is_discarded, source, owns_source, node_count, memory_usage, and shrink_to_fit. basic_json_view adds type, the is_* queries, operator bool, size, empty, materialize, and source_offset. A parse error throws the same exception basic_json::parse would throw for the same input, message and position included. detail::abi_config keeps JSON_STRICT_NUL_HANDLING and JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON readable after json.hpp undefines them, in the ABI namespace so they always match the basic_json in use. A NUL byte that ends a // comment is the end of the input, as in parse() since #5696. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
1.5 KiB
1.5 KiB
nlohmann::basic_json::is_structured
constexpr bool is_structured() const noexcept;
This function returns #!cpp true if and only if the JSON type is structured (array or object).
Return value
#!cpp true if type is structured (array or object), #!cpp false otherwise.
Exception safety
No-throw guarantee: this member function never throws exceptions.
Complexity
Constant.
Possible implementation
constexpr bool is_structured() const noexcept
{
return is_array() || is_object();
}
Notes
The term structured stems from RFC 8259:
JSON can represent four primitive types (strings, numbers, booleans, and null) and two structured types (objects and arrays).
Note that though strings are containers in C++, they are treated as primitive values in JSON.
Examples
??? example
The following code exemplifies `is_structured()` for all JSON types.
```cpp
--8<-- "examples/is_structured.cpp"
```
Output:
```json
--8<-- "examples/is_structured.output"
```
See also
- is_primitive() returns whether JSON value is primitive
- is_array() returns whether the value is an array
- is_object() returns whether the value is an object
- basic_json_view::is_structured - the same check on a zero-copy view
Version history
- Added in version 1.0.0.