callback-set with reentrant invocation

Reentrant:

1. A callback can modify parent callback-set (for example to remove itself), even while being invoked.
2. Any such re-entrant operations are deferred until callback invocation completes.

build + install

$ cd xo-callback
$ mkdir build
$ cd build
$ INSTALL_PREFIX=/usr/local  # or wherever you prefer, e.g. ~/local
$ cmake \
    -DCMAKE_MODULE_PATH=${INSTALL_PREFIX}/share/cmake \
    -DCMAKE_PREFIX_PATH=${INSTALL_PREFIX} \
    -DCMAKE_INSTALL_PREFIX=${INSTALL_PREFIX} ..
$ make
$ make install

(also see .github/workflows/main.yml)

build for unit test coverage

$ cd xo-callback
$ mkdir build-ccov
$ cd build-ccov
$ cmake \
    -DCMAKE_MODULE_PATH=${INSTALL_PREFIX}/share/cmake \
    -DCMAKE_PREFIX_PATH=${INSTALL_PREFIX} \
    -DCODE_COVERAGE=ON \
    -DCMAKE_BUILD_TYPE=Debug ..

LSP (language server) support

LSP looks for compile commands in the root of the source tree; cmake creates them in the root of its build directory.

$ cd xo-callback
$ ln -s build/compile_commands.json