mapping_overview.md

Mapping Types

The highlighted mappings below are in the daw::json namespace.

json_link

Uses deduced type mappings to determine the mapping type to use. This is also useful in systems with generic types or reflection(future or simulated). The daw_json_link_describe.h(Uses Boost.Describe for class members) and daw_json_boost_pfr_mapping.h(Uses Boost PFR library to get type members) use this mapping type.

json_array

Maps JSON arrays to C++ container types.

json_sized_array

Maps JSON arrays/size member to C++ container types. This allows easier mapping to types like unique_ptr. Precautions should be taken that the input is trusted or validated in the Constructor type to prevent resource exhaustion.

json_boolean

Maps JSON boolean values to C++ boolean/integral types.

json_class

Maps JSON objects/types to C++ types with a daw::json::json_data_contract mapping

json_custom

Maps JSON strings/literals to C++ types that don't fit.

json_custom_lit

A helper for json_custom for mapping to the non-string types

json_date

Maps JSON strings in iso8601 timestamp to values to C++ std::chrono::time_point types.

json_key_value

Maps JSON objects to C++ containers like maps or vector of pairs.

json_key_value_array

Maps JSON array of objects with key/value members to C++ containers

json_nullable

Maps JSON values that can be null to Nullable C++ std::optional or pointer like types. The _null variants of other mappings can help with this. Types are required to be Nullable via daw::json::concepts::nullable_value_traits<T>.

json_number

Maps JSON number values to C++ arithmetic/bool/enum types.

json_checked_number

Maps JSON number values to C++ arithmetic/bool/enum types but the value is checked for narrowing.

json_raw

Maps and JSON value to a C++ type. The constructor must take a character/size range and to_json_data returns raw JSON.

json_string

Maps JSON string values to C++ string types. The string type will need to own the character range they construct(no string_view).

json_string_raw

Maps JSON string values to C++ string types without processing. This allows for string_view mappings.

json_tuple

Maps JSON tuples/arrays/heterogeneous arrays to C++ class types. This requires that the order is significant. This is useful to save space because member names are not needed.

json_value

General-purpose mapping for JSON values where the type may not be predetermined.

json_variant

Maps JSON values that may be one of several types to C++ type(s). Because there is no logic specified to determine the type, only one each of JSON string, boolean, object, number, or array are allowed.

json_tagged_variant

Maps JSON values that may be one of serveral types to C++ type(s). A switcher type that inspects another member to determine which alternative is required.

json_intrusive_variant

Maps JSON values that may be one of serveral types to C++ type(s). A switcher type that inspects a sub member to determine which alternative is required.

Understanding _null and _no_name Variants

Nullable mappings end in _null

The _null variant allows the mapped value to be nullable. Useful when the JSON field may or may not be present. Maps to std::optional in C++, effectively allowing an absence of the value.

Unnamed mappings end in _no_name

The _no_name variant implies the JSON field does not have a named key in the serialized output. Typically used for JSON arrays or when the field names are not necessary. These mappings provide robust and flexible ways to handle different JSON structures and types seamlessly within C++ using daw_json_link.

Unnamed nullable mappings _null_no_name

The _null_no_name variants combine a nullable type without a name.