As of Rust 1.50 you can use bool::then:
assert_eq!(false.then(|| val), None);
assert_eq!(true.then(|| val), Some(val));
You can convert it to a Result by chaining Option::ok_or:
assert_eq!(false.then(|| val).ok_or(err), Err(err));
assert_eq!(true.then(|| val).ok_or(err), Ok(val));
As of Rust 1.62, you can use bool::then_some and pass a value directly instead of creating a closure:
assert_eq!(false.then_some(val), None);
assert_eq!(true.then_some(val), Some(val));
Alternatively, you can use Option::filter:
assert_eq!(Some(obj).filter(|_| false), None);
assert_eq!(Some(obj).filter(|_| true).ok_or(err), Ok(obj));