#[macro_use] extern crate optional_struct; #[derive(OptionalStruct)] #[opt_nested_original(LogConfig)] #[opt_nested_generated(OptionalLogConfig)] struct Config { timeout: Option, log_config: LogConfig, } #[derive(OptionalStruct)] struct LogConfig { log_file: String, log_level: usize, } #[test] fn test_apply_options() { let mut config = Config { timeout: Some(2), log_config: LogConfig { log_file: "/var/log/foobar.log".to_owned(), log_level: 3, }, }; let opt_config = OptionalConfig { timeout: None, log_config: OptionalLogConfig { log_file: Some("/tmp/bar.log".to_owned()), log_level: None, }, }; config.apply_options(opt_config); assert_eq!(config.timeout, None); assert_eq!(config.log_config.log_file, "/tmp/bar.log"); assert_eq!(config.log_config.log_level, 3); }