mirror of
https://github.com/nlohmann/json.git
synced 2026-10-04 13:40:33 +00:00
Niels Lohmann
78ddd95794
* Document GCC < 11 incomplete-type error with optional members (#3669) With GCC 10 and older in C++11/14 mode, a free to_json() for a type holding an optional<Dummy> (Dummy constructible from json) fails with "invalid use of incomplete type detector<...to_json_function...>". ADL for Dummy finds the unrelated to_json and closes an instantiation cycle through optional's converting constructor. The same error reproduces without the library, so it can't be fixed here. Add a FAQ entry explaining the cause and the hidden-friend workaround, recommend hidden friends in the arbitrary types docs, and add a regression test that keeps the workaround compiling on GCC 7-10. Signed-off-by: Niels Lohmann <mail@nlohmann.me> * Use the #3669 fixture's optional member in to_json Issue3669Holder::d is never read, so clang's -Weverything -Werror build (ci_test_clang) fails with -Wunused-private-field. Reference the member in the hidden-friend to_json; this does not affect the instantiation cycle the fixture reproduces. Signed-off-by: Niels Lohmann <mail@nlohmann.me> --------- Signed-off-by: Niels Lohmann <mail@nlohmann.me>