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Niels Lohmann ea9c4a2501 Document tools/macro_builder and tidy up serve_header.py

tools/macro_builder generates the NLOHMANN_JSON_EXPAND,
NLOHMANN_JSON_GET_MACRO and NLOHMANN_JSON_PASTE* macros in
macro_scope.hpp, but nothing referred to it. Add a README that explains
what it generates, how to run it and where the output goes, and which
dependent tables (NLOHMANN_JSON_DOUBLE_PASTE, NLOHMANN_JSON_TYPE_BODY)
are maintained by hand. Point to it from a comment above
NLOHMANN_JSON_EXPAND. The generator itself is unchanged; following the
README reproduces the header byte for byte.

In serve_header.py, drop the LGTM suppression (LGTM.com shut down in
2022), replace the """.""" placeholder docstrings with real ones, and
import socket and ssl at module level. DualStackServer.server_bind uses
socket, which was only imported under __main__; when the module was
imported instead, the NameError was swallowed and IPV6_V6ONLY was not
cleared.

The header change is a comment only; behavior, API and ABI are
unchanged.

Part of #5717

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

2026-09-30 09:45:44 +02:00

main.cpp

Reorganize directories (#3462 )

2022-05-01 09:41:50 +02:00

README.md

Document tools/macro_builder and tidy up serve_header.py

2026-09-30 09:45:44 +02:00

README.md

macro_builder

Generates the argument-counting macros behind the NLOHMANN_DEFINE_TYPE_* and NLOHMANN_DEFINE_DERIVED_TYPE_* macros in include/nlohmann/detail/macro_scope.hpp:

NLOHMANN_JSON_EXPAND
NLOHMANN_JSON_GET_MACRO, which selects a macro by the number of its arguments (64 slots)
NLOHMANN_JSON_PASTE, which calls a function-like macro for each member, and its helpers NLOHMANN_JSON_PASTE2 to NLOHMANN_JSON_PASTE64

The number of slots (max_args in main.cpp) sets the member limit of these macros. NLOHMANN_JSON_PASTE takes the function as its first argument, so 64 slots allow 63 members.

Usage

From the project root:

c++ -std=c++11 tools/macro_builder/main.cpp -o macro_builder
./macro_builder

In include/nlohmann/detail/macro_scope.hpp, replace the lines from #define NLOHMANN_JSON_EXPAND( x ) x to the #define NLOHMANN_JSON_PASTE64(...) line with the output, without its trailing empty line.
Run make amalgamate. It updates single_include/nlohmann/json.hpp and runs make pretty, which indents the continuation lines of NLOHMANN_JSON_PASTE that the tool writes unindented.

With an unchanged main.cpp, these steps reproduce the header byte for byte.

Maintained by hand

The tool does not generate everything that depends on the number of slots. When changing max_args, also update:

the NLOHMANN_JSON_DOUBLE_PASTE table right after the generated block (NLOHMANN_JSON_DOUBLE_PASTE and NLOHMANN_JSON_DOUBLE_PASTE3, NLOHMANN_JSON_DOUBLE_PASTE5, ..., NLOHMANN_JSON_DOUBLE_PASTE63), which the *_WITH_NAMES macros use
the slot table of NLOHMANN_JSON_TYPE_BODY, which chooses between the implementations for zero members and for one or more members
the documented limit of 63 members in docs/mkdocs/docs and the tests at that limit in tests/src/unit-udt_macro.cpp

Both tables pass one macro name per slot to NLOHMANN_JSON_GET_MACRO, so they need exactly as many entries as it has slots.