mirror of
https://github.com/nlohmann/json.git
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Niels Lohmann
ea9c4a2501
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>
44 lines
2.0 KiB
Markdown
44 lines
2.0 KiB
Markdown
# macro_builder
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Generates the argument-counting macros behind the `NLOHMANN_DEFINE_TYPE_*` and `NLOHMANN_DEFINE_DERIVED_TYPE_*`
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macros in [`include/nlohmann/detail/macro_scope.hpp`](../../include/nlohmann/detail/macro_scope.hpp):
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- `NLOHMANN_JSON_EXPAND`
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- `NLOHMANN_JSON_GET_MACRO`, which selects a macro by the number of its arguments (64 slots)
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- `NLOHMANN_JSON_PASTE`, which calls a function-like macro for each member, and its helpers `NLOHMANN_JSON_PASTE2`
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to `NLOHMANN_JSON_PASTE64`
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The number of slots (`max_args` in [`main.cpp`](main.cpp)) sets the member limit of these macros.
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`NLOHMANN_JSON_PASTE` takes the function as its first argument, so 64 slots allow 63 members.
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## Usage
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From the project root:
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```shell
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c++ -std=c++11 tools/macro_builder/main.cpp -o macro_builder
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./macro_builder
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```
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1. In `include/nlohmann/detail/macro_scope.hpp`, replace the lines from `#define NLOHMANN_JSON_EXPAND( x ) x` to the
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`#define NLOHMANN_JSON_PASTE64(...)` line with the output, without its trailing empty line.
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2. Run `make amalgamate`. It updates `single_include/nlohmann/json.hpp` and runs `make pretty`, which indents the
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continuation lines of `NLOHMANN_JSON_PASTE` that the tool writes unindented.
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With an unchanged `main.cpp`, these steps reproduce the header byte for byte.
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## Maintained by hand
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The tool does not generate everything that depends on the number of slots. When changing `max_args`, also update:
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- the `NLOHMANN_JSON_DOUBLE_PASTE` table right after the generated block (`NLOHMANN_JSON_DOUBLE_PASTE` and
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`NLOHMANN_JSON_DOUBLE_PASTE3`, `NLOHMANN_JSON_DOUBLE_PASTE5`, ..., `NLOHMANN_JSON_DOUBLE_PASTE63`), which the
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`*_WITH_NAMES` macros use
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- the slot table of `NLOHMANN_JSON_TYPE_BODY`, which chooses between the implementations for zero members and for one
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or more members
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- the documented limit of 63 members in `docs/mkdocs/docs` and the tests at that limit in
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`tests/src/unit-udt_macro.cpp`
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Both tables pass one macro name per slot to `NLOHMANN_JSON_GET_MACRO`, so they need exactly as many entries as it has
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slots.
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