lgi-async-extra

The API is callback-based, so the use of async.lua for composition is recommended. All callbacks receive an err value as first argument, and any non-error return values after that. The err value will be nil on success, or an error value otherwise. In almost all cases it will be an instance of GLib.Error:

read_non_existent_file(function(err, data)
    print(err) -- or `print(err.message)`
    assert(err.domain == Gio.IOErrorEnum)
    -- Checking the error code against a constant is the recommended way,
    -- but a bit verbose, due to LGI's mapping.
    -- See https://github.com/pavouk/lgi/blob/master/docs/guide.md for explanation on this mapping.
    assert(err.code == Gio.IOErrorEnum[Gio.IOErrorEnum.NOT_FOUND])
end)